Bolt Torque Calculator
Convert between wrench torque and bolt clamping force in one step. Enter your bolt material, diameter, and lubrication — or your target torque — and get the tightening torque, an assembly range, and a grade strength check on the same screen.
Input Parameters
The force the joint needs — what the bolt must squeeze the plates with.
Required Tightening Torque
50.00 N·m
same torque: 36.88 lbf·ft
How this was computed
T = K × F × d × (1 − l/100)
= 0.2 × 25,000 N × 0.0100 m × (1 − 0/100)
K and the lubrication factor l fold thread pitch, face friction, and finish into one model — it is the standard short-form used across the industry. K values here are valid for bolts from 1/4" to 1" (M6–M24); outside that range, test your hardware.
Assembly Torque Range
Real joints never see one torque. Friction scatters batch to batch and every wrench has its own accuracy — this band shows the honest window around your target.
Min Torque
36.00 N·m
preload 18.00 kN
Max Torque
66.00 N·m
preload 33.00 kN
Bolt Strength Check
Does your clamping force sit inside a safe preload on this bolt grade? The check compares bolt stress against yield and against a target preload percentage, shows the utilization ratio, and estimates how far the bolt elastically stretches over the grip length you enter.
What Is Bolt Torque?
Torque is a measure of the conversion of linear force to rotational force at some distance from the axis of rotation. When applied to a bolt, this force becomes tension in the bolt threads, which in turn applies a clamping force between the two materials being bolted together. That clamping force — not the torque itself — is what holds a joint together, resists slipping, and keeps vibration from shaking the fastener loose.
The amount of tension in the bolt is significant. For each application there is an ideal bolt torque value. Apply too little torque and vibrations will tend to loosen the bolt over time, which may result in joint failure. The joint may also slip or open under load long before anything visibly "loose" appears.
Apply too much torque and the bolt may yield — stretch past its elastic limit — causing the clamping force to actually reduce. Increase the torque still further and the bolt may break during assembly or, even worse, later in service while the machine is running. This is why the tightening torque matters both ways: it is the single control variable a technician has at the wrench, and it has to land inside a window, not on one perfect number.
Bolt torque values range from around 4 to 300 lbf·ft (5 to 400 N·m) for common hardware, depending on the bolt material, its diameter, and how much lubrication is applied. A torque value printed on an assembly drawing almost always assumes a specific bolt grade, a specific finish, and a specific lubrication state — change any one of those three and the correct torque changes with it.
Bolt Tightening Torque Calculation Formula
The conversion from torque to clamping force depends on the bolt material, its diameter, and how much lubrication is applied. Here is the formula that takes these factors into account and relates bolt torque and clamping force:
T = K × F × d × (1 − l/100)
- T is the torque applied by the wrench to tighten the bolt (N·m or lbf·ft);
- K is a constant factor that takes into account bolt material, finish, and size — the "nut factor";
- F is the clamping force the bolt applies to the surfaces being bolted (N or lbf);
- d is the nominal diameter of the bolt (m or ft) — the body, not the head;
- l is the amount of lubrication, given as a percentage.
You should note that this formula is only an approximation, as it does not take into account the bolt thread pitch — the angle and density of threads. Every real joint hides friction that varies with surface condition, plating thickness, and speed of tightening, which is why the same bolt can need different torques on Monday and Friday. The K constant absorbs most of that variation when it comes from test data on hardware like yours, and the assembly range panel on this page shows the honest scatter around the result.
The same equation runs in reverse. If you know the torque — because a wrench is what you can actually set — you can solve for the clamping force the joint will see: F = T / [K × d × (1 − l/100)]. That is the second calculation mode in the tool above, and it is the more honest direction in practice: wrenches control torque, joints experience force.
How to Use This Bolt Torque Calculator
The tool works both ways — it can act as a bolt torque calculator when you know the force, and as a bolt clamping force calculator when you know the torque. Note that by changing the calculator units, it is both a metric bolt torque calculator and an imperial bolt torque calculator. You can even use mixed units if you like: pick the force in lbf and read the torque in N·m if that is how your bench is set up.
- 01Set the constant K that depends on the bolt material. Either choose from the bolt types listed, or if you know the value of K for the bolts you are using, select "Enter a custom constant K" and type it in. Note that the K values for the different bolt types are valid for bolts between 1/4" and 1".
- 02Input the diameter of the bolt. To be clear, that is the body of the bolt, not its head. Pick a preset size from the dropdown or type a custom diameter, then choose the thread series — coarse or fine (UNC/UNF on the imperial side) — since the stress area and preload numbers in the strength check follow that choice.
- 03In the lubrication section, either select one of the available lubricants or directly input the lubrication factor for your lubricant by choosing the custom option. When in doubt, dry assembly is the conservative choice for the bolt but the pessimistic one for your wrist.
- 04Finally, to calculate the torque required when tightening the bolt, enter the clamping force needed for your application. Or — if you know the bolt torque required, switch the mode, enter its value, and the calculator will compute the clamping force.
- 05Read the two bonus panels under the main result: the assembly torque range, which widens your answer by friction scatter and tool accuracy, and the strength check, which verifies the bolt grade can carry the preload, estimates the bolt's elastic stretch over your grip length, and offers one-click copying of the results for your work log.
Example: Torque for a Zinc-Plated Bolt
Let's do the bolt torque calculation on paper so you can check the tool. Say you have a zinc-plated mild-steel bolt with a diameter of 3/4 inch (or 1/16 ft), lubricated with SAE 30 oil (40% lubrication factor). The specification for this bolt fixing says the clamping force needs to be 25,000 lbs.
Putting all of that into the tightening torque formula gives:
T = K × F × d × (1 − l/100)
= 0.2 × 25,000 lb × 1/16 ft × (1 − 40/100)
= 187.5 lbf·ft
Run the same numbers in the calculator — switch it to imperial, pick "zinc-plated", type 0.75 in for the diameter, choose SAE 30 oil, and enter 25,000 lbf — and you will get exactly 187.5 lbf·ft. The strength check will also flag that 25,000 lbf is a serious preload: on a grade 5 bolt of that size it lands near 85% of yield, which is why lubricated assembly and a calibrated wrench matter at this scale.
If instead you had run the bolt dry (l = 0), the same joint would demand 312.5 lbf·ft — two thirds more torque for the same clamp. That gap is the lubrication factor at work, and it is the single most common mistake in shop torque practice: using a dry value on an oiled bolt over-tightens by exactly that ratio.
K Constant Values by Bolt Type
The nut factor K compresses everything frictional about a bolted connection — thread angle, pitch, helix, and the two friction interfaces — into one number. The values below are the classic handbook set for mild-steel fasteners between 1/4" and 1", extended with the surface treatments, lubricants, and thread lockers that show up in real shops. They are the same values the calculator dropdown draws on, and they match the worked example above.
| Surface / Lubricant | Constant K | Typical Situation |
|---|---|---|
| Dry, rusty / weathered | 0.25 | Corroded threads — torque swings wildly; clean the hardware instead of trusting a K |
| Dry galvanized | 0.22 | Hot-dip or mechanical galvanizing — rough zinc raises friction noticeably |
| Mild steel, dry | 0.20 | Clean bare threads, as-delivered, no added lubricant |
| Zinc-plated, dry | 0.20 | Standard electroplated hardware — the common shop bolt |
| Black finish, dry | 0.30 | Black oxide / unfinished bolts, rougher friction surfaces |
| Phosphate & oil | 0.17 | Phosphate coating with a light oil film, common on OEM fasteners |
| Cadmium-plated | 0.16 | Smooth plating with naturally low friction |
| Machine oil | 0.16 | Light oil film on threads and nut face |
| Lubricated mild steel | 0.15 | General-purpose oil or thread compound on threads and nut face |
| Graphite in mineral oil | 0.14 | Classic high-temperature thread lubricant |
| Lithium grease | 0.13 | Common multi-purpose shop grease |
| Loctite 222 (green) | 0.10 | Low-strength thread locker for small fasteners |
| Loctite 242 (blue) | 0.12 | Medium-strength thread locker — the shop standard |
| Loctite 263 (red) | 0.14 | High-strength locker; heat is needed for removal |
| Copper anti-seize paste | 0.12 | Copper-graphite paste for high-temp service and stainless galling |
| MoS₂ (moly) paste | 0.11 | Molybdenum disulfide — high-pressure boundary lubrication |
| PTFE-based lubricant | 0.10 | Dry-film or PTFE sprays, very low friction |
| Nickel anti-seize | 0.09 | Premium anti-seize for stainless and extreme temperature — torque drops sharply |
| Wax assembly paste | 0.08 | Premium assembly pastes — the lowest published K values |
Lubrication factors used by the tool: no lubricant 0%, graphite in mineral oil 25%, white grease 35%, SAE 30 oil 40%, SAE 40 oil 30%. If your lubricant publishes a torque-reduction figure, enter it directly as a custom factor — published values from the lubricant manufacturer always beat generic tables. Thread lockers deserve a special note: they add "prevailing torque" that consumes part of the wrench input before the joint even clamps, so their K values already include that penalty — but always torque them to spec while the compound is wet and let the full cure time elapse before loading the joint.
Typical Bolt Torque Chart — 75% Preload
The chart below is generated from the same formulas the calculator runs — nothing is typed in by hand. It assumes 75% of yield as the preload target (class 8.8 for metric, grade 5 for imperial) on standard coarse threads, and shows both a dry and a lubricated torque so you can see the lubrication gap size by size. For a class 10.9 or grade 8 bolt, multiply the torque by roughly 1.5; for class 4.6 or grade 2, by roughly 0.4.
| Size | Stress Area (mm²) | Clamp Force @ 75% (kN) | Torque, dry K=0.2 (N·m) | Torque, oiled K=0.15 (N·m) |
|---|---|---|---|---|
| M5 | 14.183 | 6.8 | 6.8 | 5.1 |
| M6 | 20.123 | 9.7 | 11.6 | 8.7 |
| M8 | 36.608 | 17.6 | 28.1 | 21.1 |
| M10 | 57.989 | 27.8 | 55.7 | 41.8 |
| M12 | 84.266 | 40.4 | 97.1 | 72.8 |
| M16 | 156.668 | 75.2 | 240.6 | 180.5 |
| M20 | 244.794 | 117.5 | 470.0 | 352.5 |
| M24 | 352.503 | 169.2 | 812.2 | 609.1 |
| M30 | 560.586 | 269.1 | 1,614.5 | 1,210.9 |
Chart values are computed, not transcribed: they follow ISO 898-1 / SAE J429 minimum strengths and the tensile stress areas of standard coarse threads. They are suitable for planning and cross-checking — but a joint with a published specification should always follow that specification.
Preload, Bolt Grades, and the Strength Check
Torque is only a means to an end — the end is preload, the tension stretched into the bolt like a stiff spring. Structural practice tightens structural bolts to about 75% of yield because at that point the joint has strong vibration resistance and the bolt still keeps elastic reserve. Permanent connections pushed to 90% squeeze harder but leave little margin for over-torque, which is why the preload slider on this page stops there.
The capacity check divides your clamping force by the bolt's tensile stress area — the effective area at the threaded section, which is smaller than the shank and therefore governs. For metric threads, As = π/4 · (d − 0.9382·P)² where P is the thread pitch; for unified threads, As = π/4 · (d − 0.9743/n)² where n is threads per inch. Bolt stress is that force divided by the area, and the utilization ratio is the stress against the grade's minimum yield: 640 MPa for class 8.8, 92 ksi for grade 5, 130 ksi for grade 8, and so on.
Thread series matters here too. A fine thread (or UNF on the imperial side) raises the tensile stress area at the same nominal diameter — an M10 fine thread gives about 61 mm² against 58 mm² coarse, and a 1/2"-20 UNF about 0.160 in² against 0.142 in² for coarse — which lifts both the preload the bolt can carry and the torque needed to reach a given percentage of yield. The thread-series selector under the diameter input feeds the same stress-area formulas, and the strength check numbers move accordingly. The torque model itself does not change: K already absorbs the friction differences between series, which is why the same K value serves both.
Beyond stress, experienced assemblers track how far the bolt actually stretches, because stretch is the most direct read on preload: ΔL = F·L/(E·A), with E ≈ 210 GPa for carbon and alloy steel, L the grip length (head seat to nut face), and A the tensile stress area. A class 8.8 M12 at 40 kN over a 40 mm grip, for example, stretches about 0.09 mm — hundredths of a millimeter, which is why length-based tightening needs micrometer-grade measurement and why torque remains the everyday control method. The strength check panel estimates this value from your grip length so you can sanity-check joint stiffness: the bolt is the spring, and a longer grip or smaller area means more stretch for the same force.
Read the check the way an engineer would. A utilization under 75% means the joint is fine but possibly under-preloaded against vibration; between 75% and 90% is exactly where structural preload lives; above 100% the bolt yields during assembly and the clamp force you calculated never actually develops. If the check fails, the escapes are familiar ones: a higher grade, a larger diameter, more bolts sharing the load, or better friction control so the torque you apply actually converts to clamp instead of heat.
Rule of thumb
Only about 10% of wrench torque stretches the bolt — the other 90% is friction at the threads and under the nut face. Anything that changes friction (plating, oil, thread locker, washers) changes the preload you get from the same torque. That is why torque specs name the lubricant, and why the strength check on this page lets you verify the joint rather than trust the wrench.
Bolt Grade Strength Chart — ISO 898-1, SAE J429 & ASTM
Every bolt head carries a grade mark, and every grade mark is a promise about strength. Metric bolts use property classes under ISO 898-1: two numbers where the first is the minimum tensile strength in hundreds of megapascals and the second is the yield ratio. A class 8.8 bolt therefore has a minimum tensile strength of 800 MPa and a yield strength of 0.8 × 800 = 640 MPa. Imperial bolts follow SAE J429 and ASTM specifications, where the numbers are simple escalators — grade 5 is stronger than grade 2, grade 8 stronger still — and the actual values come from the standard's tables, which is exactly what the chart below restates.
| Grade | Yield (min) | Tensile (min) | Typical Use |
|---|---|---|---|
| Metric — ISO 898-1 property classes | |||
| Class 4.6 | 240 MPa | 400 MPa | Light-duty general hardware — consumer assemblies, low-load frames |
| Class 4.8 | 320 MPa | 420 MPa | General machine hardware where loads stay modest |
| Class 5.6 | 300 MPa | 500 MPa | Medium-duty metric fasteners with better ductility than 5.8 |
| Class 5.8 | 420 MPa | 520 MPa | The everyday high-tensile hardware-store bolt |
| Class 6.8 | 480 MPa | 600 MPa | Machinery and automotive fasteners in the mid-strength band |
| Class 8.8 | 640 MPa | 800 MPa | The metric structural workhorse — rough equivalent of SAE grade 5 |
| Class 9.8 | 720 MPa | 900 MPa | More preload in the same footprint; common in automotive assemblies |
| Class 10.9 | 940 MPa | 1040 MPa | Heavy equipment, press frames, high-strength joints (≈ SAE grade 8) |
| Class 12.9 | 1100 MPa | 1220 MPa | Maximum commercial strength — high-performance machinery and racing |
| Imperial — SAE J429 / ASTM | |||
| SAE Grade 2 | 57 ksi | 74 ksi | Everyday low-strength imperial hardware (≈ class 4.8–5.8 territory) |
| SAE Grade 5 / ASTM A325 | 92 ksi | 120 ksi | The imperial workhorse — automotive, machinery (≈ class 8.8) |
| SAE Grade 8 | 130 ksi | 150 ksi | High-strength imperial — heavy trucks, suspension (≈ class 10.9) |
| ASTM A307 (Gr A) | 36 ksi | 60 ksi | Anchor bolts and light structural work where strength is not critical |
| ASTM A490 | 130 ksi | 170 ksi | Heavy structural connections — bridges and building frames |
The imperial–metric overlaps are worth memorizing: SAE grade 5 and class 8.8 are close enough to substitute in most non-critical work, and grade 8 pairs with class 10.9. What never substitutes is mixing systems inside a preload calculation — a bolt tightened to the other system's table can land 20–30% away from its intended clamp.
The Preload Target Ladder
Once the grade is known, the second decision is how hard to stretch the bolt. The ladder below mirrors the preload slider in the calculator, with the shorthand labels assembly engineers use for each band:
| % of Yield | Label | Where It Belongs |
|---|---|---|
| 50% | Minimal | Soft gaskets, thermoplastic housings, joints you retighten often |
| 60% | Conservative | General machine assembly when friction data is uncertain |
| 70% | Standard | A safe default when no specification calls out a target |
| 75% | Structural | AISC-style steel-to-steel practice — the torque chart below uses this |
| 80% | Elevated | Controlled lubrication and calibrated tools; the bolt stays elastic |
| 85% | Heavy-duty | Verified friction data and monitored power assembly |
| 90% | Maximum | Permanent connections only — almost no reserve against over-torque |
Grades are minimums by specification: a real batch of class 8.8 bolts usually tests well above the table values, but design to the minimum — that is what the grade mark promises, and what the strength check on this page uses.
What Torque Doesn't Cover: Shear, Bearing, and Fatigue
Torque sets the clamp, but it says nothing about how the joint carries external load once assembled. Bolts in real structures see three very different situations: tension along the shank — which the strength check on this page covers — shear across it, and, the one that surprises people, almost no load at all, because friction between the clamped plates takes the force before it ever reaches the bolt. A well-preloaded joint is designed around that third situation: the plates slip-fight through friction, and the bolt mostly holds the press.
A lap joint puts the bolt in single shear: one plane between the plates, with stress τ = F / A. Add a third plate and the same bolt works in double shear — two planes share the load, and the stress per plane halves. The formula generalizes to n bolts and m shear planes:
τ = F / (n × m × A)
The same equation covers pins, rivets, and clevises — anything loaded across its shank. What changes between materials is how much shear they forgive:
Two shop rules close the loop. Keep thread engagement at least 1.5 × d in steel — 2 to 2.5 × d into aluminum — or the female thread strips before the bolt itself yields. And remember that the governing failure may not be the bolt at all: thin plates fail by bearing at the hole, by tearout toward the edge, or by block shear pulling out a corner of the plate. Professional connection checks run all four limits — bolt shear, bearing, tearout, block shear — and the lowest one governs, which is why a bolt that passes the stress check can still fail the joint.
| Bolt Material | Ultimate Shear | Static Allowable | Fatigue Allowable |
|---|---|---|---|
| Carbon & alloy steel | 200–400 MPa | ≈ 120–320 MPa | ≈ 60–200 MPa |
| Stainless (304 / 316) | 150–300 MPa | ≈ 90–240 MPa | ≈ 45–150 MPa |
| Aluminum (2024 / 7075) | 100–200 MPa | ≈ 60–160 MPa | ≈ 30–100 MPa |
Static allowable assumes about 60–80% of the ultimate shear strength; under cyclic load the safe band drops to 30–50%, and safety factors of 2–4 (up to 10 for safety-critical dynamic hardware) are applied on top. Design codes are stricter still: AISC allows 0.62 × Fu per shear plane with threads excluded from the plane and 0.48 × Fu with threads included — our bolt shear calculator implements exactly that.
Fatigue: more preload, not less
Under cyclic load a bolt can fail far below its static allowable — and the remedy is counterintuitive. A well-preloaded joint keeps the plates pressed together, so load swings travel through friction and the plates rather than cycling stress into the bolt. That is why fatigue-critical assemblies torque bolts to 75% of yield, then add thread lockers or prevailing-torque nuts on top.
Run the full shear check
The companion shear calculator implements the AISC allowables — single and double shear, thread condition, multiple bolts, and safety factors.
Torque Control vs. Turn-of-Nut, Tensioners, and Stretch
Torque control wins on cost and speed, and loses on honesty: because roughly 90% of the wrench input goes to friction, preload scatter of ±20–30% is normal even with careful practice. When a joint cannot tolerate that scatter, engineers pay for methods that measure something closer to the actual stretch of the bolt. Each step up the ladder trades money and setup time for preload accuracy:
| Method | How It Works | Preload Scatter | Where It Wins |
|---|---|---|---|
| Torque control (wrench) | Measures applied torque; preload is inferred through friction | ±20–30% | The default for most assemblies — cheapest, fastest, and every shop owns a wrench |
| Turn-of-nut (angle) | Snug fit, then a prescribed rotation; partly insensitive to friction | ±10–15% | Structural steel (A325 / A490) and bridge work |
| Torque–angle yield control | Power tool tracks the torque curve slope and stops at yield onset | ±7–10% | Automotive critical joints — engine heads, connecting rods |
| Hydraulic tensioner | Pulls the bolt directly; the nut runs down unloaded | ±5–10% | Large diameters (1" and up) — flanges, pressure vessels |
| Bolt heating / stretch | Heat-extends the stud or measures stretch; nut set by hand | ±3–5% | Very large studs — turbines, presses, forging equipment |
The escalation logic is simple: the more critical the joint and the bigger the bolt, the more sense the direct methods make. Below about one inch of diameter, torque wrenches and angle control cover nearly everything — which is why the tool on this page exists and why the assembly range panel is honest about its limits. Flanged pressure equipment lives on hydraulic tensioners, and turbine studs — four inches of alloy steel and stakes measured in whole machines — get heated, stretched, and snugged by hand against measured elongation.
Whatever the method, the joint still wants the same thing: a preload inside the window this calculator brackets for you. Use the range panel as the acceptance band for whichever tightening method your shop can afford.
Tap Drill & Clearance Hole Chart for Common Threads
The torque chart is only half the fastener story — the other half is drilled. A tapped hole needs a pilot sized so the female thread has full height: about 75% thread is the shop standard, because a larger pilot weakens the bolt's engagement while a smaller one overloads the tap. A through hole, meanwhile, needs clearance for assembly without letting the bolt head dig in. Clearance holes come in three fits — close for located assemblies, normal as the everyday default, and coarse / free for covers and slightly misaligned parts (ISO 273 on the metric side, ASME B18.2.8 in imperial).
Metric coarse threads
| Thread | Tap Drill (mm) | Close Fit | Normal Fit | Coarse Fit |
|---|---|---|---|---|
| M5 × 0.8 | 4.2 | 5.2 | 5.5 | 5.8 |
| M6 × 1.0 | 5.0 | 6.4 | 6.6 | 7.0 |
| M8 × 1.25 | 6.8 | 8.4 | 9.0 | 10.0 |
| M10 × 1.5 | 8.5 | 10.5 | 11.0 | 12.0 |
| M12 × 1.75 | 10.2 | 13.0 | 13.5 | 14.5 |
| M16 × 2.0 | 14.0 | 17.0 | 17.5 | 18.5 |
| M20 × 2.5 | 17.5 | 21.0 | 22.0 | 24.0 |
Unified coarse threads (UNC)
| Thread | Tap Drill (in) | Close Fit | Normal Fit | Loose Fit |
|---|---|---|---|---|
| 1/4" – 20 UNC | #7 (0.201") | 17/64 (0.266) | 9/32 (0.281) | 5/16 (0.313) |
| 5/16" – 18 UNC | F (0.257") | 21/64 (0.328) | 11/32 (0.344) | 3/8 (0.375) |
| 3/8" – 16 UNC | 5/16 (0.3125") | 25/64 (0.391) | 13/32 (0.406) | 7/16 (0.438) |
| 1/2" – 13 UNC | 27/64 (0.422") | 33/64 (0.516) | 17/32 (0.531) | 9/16 (0.563) |
| 5/8" – 11 UNC | 17/32 (0.531") | 41/64 (0.641) | 21/32 (0.656) | 3/4 (0.750) |
| 3/4" – 10 UNC | 21/32 (0.656") | 49/64 (0.766) | 25/32 (0.781) | 7/8 (0.875) |
Both charts assume standard coarse threads. Fine threads shift only the tap drill upward — M10 × 1.25 taps at 8.75 mm instead of 8.5 mm — while clearance holes stay put. In soft materials like aluminum, tapping a size larger keeps full thread depth with less tap breakage; in hard alloy steel, stay on the chart.
Bolt Calculator App, Metric Torque Data & Excel Workflows
Everything above runs as a bolt calculator app in your browser — no installer, no account, no spreadsheet. Three questions come up most when the tool moves into daily work: how the app behaves on phones and shop tablets, exactly what the metric bolt torque calculator covers from M3 upward, and how to hand the same numbers to a client who lives in Excel. Each answer below runs on the identical T = K·F·d engine as the calculator.
Using the bolt calculator app on any device
The bolt calculator app is simply this page, so it behaves like a native tool everywhere a modern browser runs — iPhone, Android, iPad, a shop-floor tablet, or a laptop back at the desk. Every keystroke recalculates locally on the device: no inputs are uploaded, no login is required, and nothing is stored once you close the tab. On a phone, add it to your home screen and it opens full-screen like an installed app; on a shared workstation, the bookmark is the install. The unit toggle, thread-series selector, and sliders are all sized for touch, which matters more than it sounds when you are holding a wrench in the other hand.
Metric bolt torque calculator: M3 to M48 in N·m
The bolt calculator, metric first, ships with every ISO coarse size from M3 to M48 — M6, M8, M10, M12, M16, and M20 come preloaded with correct stress areas — and the thread-series selector adds fine pitches such as M10×1.25 and M12×1.5. Torque comes out in N·m with clamping force in kN, the strength check grades the bolt against ISO 898-1 classes 8.8 through 12.9, and the K-factor table covers the finishes you actually meet on metric hardware: black oxide, zinc plate, phosphated, lightly oiled. Flip the unit toggle and each metric size snaps to its nearest imperial neighbor — M10 becomes 3/8" — so mixed fleets of hardware stay one calculation away.
Bolt torque calculator Excel sheet: three ways to get the data
Plenty of specs still ask for numbers in a spreadsheet, and this page works as a bolt torque calculator Excel alternative in three ways. First, the Copy results button under the main output pastes a formatted line straight into any cell. Second, the 75% preload torque chart above prints cleanly on one sheet for the job box. Third — if your process genuinely requires a workbook — build one row per bolt with the formula below, then sanity-check a few rows here, because a spreadsheet freezes a single K value per row and quietly forgets the ±20–30% friction scatter the live tool displays as a torque range.
Building your own torque sheet?
One row per bolt needs four columns: diameter d in meters, clamping force F in newtons, nut factor K, and lubrication l in percent. Torque in N·m is then T = K × F × d × (1 − l/100), and multiplying by 1.05–1.25 gives the wrench range band. That single formula is the entire engine — the same math this page runs on every keystroke, minus the rounding errors hand-typed sheets collect.
Start From Your Project, Not From a Blank Calculator
Every calculator page pairs a focused tool with the tables, formulas, and real-world numbers that make each result trustworthy. Pick the task, enter your fastener and joint details, and read the answer — with the reasoning behind every number kept in plain sight.
Bolt Shear Calculator
Check bolt shear stress with interactive sliders: bolt count, diameter, single or double shear, grade-based allowable stress and pass/fail safety check.
Get the numbersBolt Weight Calculator
Weigh a complete fastener set: hex bolt plus nut and washer options, per-piece and total weight by quantity. Free, instant, no sign-up.
Get the numbersDeep-Dive Guides & How-Tos
Step-by-step walkthroughs, material comparisons, pro tips, and real-world case studies — everything you need to plan, estimate, and tighten with confidence.
The first guides are in the works — step-by-step tightening procedures, grade comparisons, and joint-design walkthroughs will appear here as each one is published.
Read all guidesBolt Torque FAQ
The questions this calculator gets asked most, answered with the same formulas the tool runs.