Bolt Shear Stress Calculator
Check whether a bolt group can carry a lateral load in shear. Set the diameter, bolt count, and grade with interactive sliders, choose single or double shear, and read the shear stress, the grade-based allowable, and a PASS/FAIL utilization check — live on every keystroke.
Input Parameters
The sideways load the whole bolt group must transfer between the plates.
Threads included → 0.48 × Fu · threads excluded → 0.62 × Fu (AISC-style).
1.5 for known static loads, 2 for general machine design, 3+ for uncertain or safety-critical joints.
Shear Stress per Bolt
110.5 MPa
= 16.03 ksi · avg. stress on one shear plane
How this was computed
τ = F / (n × A × m)
= 50,000 N / (4 × 113.10 mm² × 1) = 110.5 MPa
A is the gross nominal shank area π/4·d² — the standard area for hand shear checks. The thread penalty is applied on the allowable side (0.48 vs 0.62 × Fu), not by shrinking the area.
Results Detail
Every intermediate value behind the verdict, so you can carry it into a report or check it with a hand calculator.
What Is Bolt Shear Stress?
When a load pushes perpendicular to a bolt's axis — a bracket holding a swinging mass, a gusset plate bracing a column, a linear actuator mount reacting side thrust — the bolt is loaded in shear. The two joined plates try to slide past each other, and the bolt bridges them like a pin. The cross-section of the bolt at the interface between the plates is what resists that sliding, and the average stress on it is the bolt's shear stress:
τ = F / (n × A × m)
- τ is the average shear stress in each bolt (MPa or ksi);
- F is the total lateral load shared by the bolt group (N, kN, or lbf);
- n is the number of bolts that share the load equally;
- A is the cross-section area of one bolt, π/4 · d², from the nominal diameter d;
- m is the number of shear planes per bolt — 1 in single shear, 2 in double shear.
Shear failure and tension failure are different animals, and they are checked with different areas. A bolt in tension stretches along its axis, necks, and finally breaks at the weakest section — the threaded portion, which is why tension checks use the smaller tensile stress area at the thread root. A bolt in shear is cut like a punch: the load acts across the shank, perpendicular to the axis, and the section that matters is the nominal area π·d²/4. The failure modes look different too. Tension failure is usually preceded by visible elongation; a well-fitted shear joint can go from intact to cleanly severed with almost no warning. That asymmetry is why a bolt that passes a tension check can still fail in shear — and why a joint loaded in both directions needs both checks plus their interaction.
Shear fractures run straight across the shank at the shear plane, looking almost sawn. Because the failure is sudden, design codes keep a respectful distance from it: instead of allowing stress up to yield, the allowable values are anchored to the ultimate tensile strength Fu of the grade with a further reduction (0.62 or 0.48 — covered in the next section). Yield in shear is hard to define, and deformation-based limits are impractical to inspect, so the ultimate-strength anchor gives a limit state you can actually verify: cut a sample bolt, measure the fracture, confirm the grade.
For a feel of the numbers: a single M12 class 8.8 bolt has a shank area of about 113 mm² and an allowable shear stress near 496 MPa with the threads excluded from the plane, so one bolt carries roughly 56 kN in single shear before the allowable is even reached. The same bolt in a clevis — double shear — handles about twice that. Run your own geometry in the calculator above and the utilization bar tells you instantly how close the joint is to its limit.
Single Shear vs Double Shear
In a single shear joint — a plain lap joint — the two plates overlap and the load passes from one plate into the bolt and out the other across exactly one interface. The full load on each bolt acts on one cross-section, so m = 1. It is the simplest and cheapest arrangement, and it is everywhere: angle brackets, one-sided splice plates, hanger rods, actuator mounts bolted to a face plate. The catch is eccentricity. Because the load path is offset, a lap joint also bends the bolt slightly, and that secondary bending stress sits on top of the shear stress this calculator reports. Snug fit and a short overhang keep it small; a long cantilevered bracket can make it govern.
A double shear joint sandwiches the middle member between two outer members — a clevis, a U-bracket, a double gusset. The same load now has two interfaces to cross, so each bolt cross-section carries half of it: m = 2. Doubling the effective area halves the stress for the same load, which means double shear roughly doubles the shear capacity of every bolt in the group. That is why heavily loaded pins, lifting lugs, and actuator clevises almost always use the three-plate arrangement — the second plate is the cheapest capacity you will ever buy.
The diagrams above show the load path: in single shear the two plates pull in opposite directions across one plane; in double shear the center plate pulls one way while the two outer plates pull the other, sharing the load across two planes. Two practical caveats before you bank the factor of two. First, the share is only equal if the joint is snug — a sloppy clevis can load one plane first, and the calculator's even-split assumption then flatters the real stress. Second, the bolt is rarely the only thing to check: the plates themselves see bearing stress under the bolt and tear-out at the edges, and on thin plates those checks often govern before bolt shear does.
Allowable Shear Stress & Bolt Grades
The calculator compares the computed shear stress against an allowable shear stress, FnV, derived from the bolt grade's minimum ultimate tensile strength Fu the way structural steel codes (AISC 360-style) do it: 0.62 × Fu when the threads are excluded from the shear plane, and 0.48 × Fu when the threads are included. Both factors look low next to the 0.75–0.8 you might expect for a material limit — deliberately so. Shear capacity is anchored to ultimate rather than yield because shear deformation before fracture is large, hard to define, and impossible to inspect in a finished joint.
The threads-included case deserves a closer look. A thread root has roughly 75–80% of the shank's effective area, so a plane that cuts through threads shears a smaller section. Rather than tracking two areas, codes fold the reduction into the stress limit: 0.48 ≈ 0.62 × 0.78. Practically, that means you recover about 29% more allowable stress just by positioning the joint so the shear plane crosses the plain shank instead of the threads — a grip-length detail that costs nothing at design time and nothing at assembly if the spec calls it out.
The table below is generated from the same grade data the calculator uses — nothing is typed in by hand — and follows your metric/imperial selection. Your utilization is then simply the computed stress times the safety factor, divided by the applicable allowable value.
| Grade | Ultimate Fu (MPa) | Allowable, threads excluded — 0.62Fu (MPa) | Allowable, threads included — 0.48Fu (MPa) |
|---|---|---|---|
| Class 8.8 | 800 | 496 | 384 |
| Class 10.9 | 1,040 | 645 | 499 |
Values are minimum specified ultimate strengths from ISO 898-1 (metric classes) and SAE J429 / ASTM (imperial grades), run through the same 0.62 / 0.48 factors the calculator uses. A full structural design adds joint-level checks — bearing on the plate, tear-out, edge distance, and combined shear plus tension — that this table intentionally does not cover.
Safety Factor Guide
The allowable shear stress already contains one margin — it is a fraction of ultimate strength, not the strength itself. The safety factor slider applies a second, explicit margin on the demand side: utilization = τ × SF / FnV. Why two margins? The code factor covers scatter in material strength and workmanship across a whole industry. Your safety factor covers everything specific to your application — how well you know the load, what a failure would cost, and how the load is applied. The slider lands on 1.5 by default; here is where each setting earns its keep.
1.5×
Known static loads
Design loads from a datasheet or a measured duty cycle, applied smoothly: actuator mounts, fixtures, brackets with a defined working load. A common preliminary-design value — and this calculator's default.
2.0×
General machine design
Recurring shock, frequent starts and stops, or loads you estimated rather than measured. The classic textbook default for machine members under ordinary uncertainty.
3.0×
Uncertain or safety-critical
Impact and vibration you cannot characterize, lifting gear, personnel platforms, and any joint whose failure hurts someone. If you cannot defend the load estimate, raise the factor instead.
Two honest warnings. A big safety factor does not rescue a wrong grade or a corroded bolt — it only scales a stress number. And because the factor multiplies the demand, not the capacity, its effect is direct: raising the factor from 1.5 to 3.0 exactly doubles the utilization, so a joint sitting at 55% at SF 1.5 is already over the line at SF 3.0. When a check fails, work the levers in order of cost: switch to double shear, add a bolt or two, step up one diameter, then jump a grade. Changing the geometry is almost always cheaper than changing the hardware.
Bolt Shear FAQ
The questions this calculator gets asked most, answered with the same formulas the tool runs.
How do you calculate shear stress in a bolt?
Is a bolt stronger in single or double shear?
What is the allowable shear stress of a class 8.8 bolt?
Why is the capacity lower when threads cross the shear plane?
What safety factor should I use for bolt shear?
Which area does this calculator use — shank or threaded?
Does bolt preload or friction change the shear load?
Can I switch between metric and imperial?
Related Bolt Calculators
Shear is one link in the fastener chain — check the torque and tension side of the same joint with the companion tools.