Bolt torque calculator

This is not another number toy. Bolt torque calculator replaces the guessing with an actual computation, and the notes below explain what to do with the result.

Nothing you type here leaves your browser. Being roughly right about the inputs beats being precisely wrong about them.

What it actually does

On technical fasteners errors are paid immediately: too little torque means a loose joint; too much means stripped threads or a cracked head. Every figure above applies to Canada specifically and is reviewed when the rules change. Bolt torque Canadian calculation tool turns bolt, screw and nut specs into concrete numbers — torque, shear load, preload, weight. The number pair encodes tensile strength (8.8 = 800 MPa tensile, 640 MPa yield).

Amounts on this page use Canadian dollars and metric units, with provincial variation noted where it matters. For Canada, use the units printed beside each field and do not assume that a familiar name means the same measurement system.

The numbers behind the number

Example: a M10 class 8.8 bolt at friction coefficient 0.15 requires a specific torque in Nm. For repeatedly disassembled joints — use self-locking nuts or spring washers. DIN 931 (ISO 4014) — partial thread (plain shank under the head). Use before assembling a critical structure, when writing an engineering spec, when checking a torque-wrench installation, when computing weight for shipping, or when picking the right property class for the application.

For M10 8.8 that's about 47 Nm dry, ~35 Nm lubricated. Lubrication cuts required torque 20–30% because less friction means the same torque delivers higher preload.

When it makes sense to reach for this

Only with designer approval. DIN 933 (ISO 4017) — fully threaded.

Use 931 for shear joints, 933 for tension. Down-substitution risks shear failure or loosening.

10.9 is 25% stronger tensile and used in preloaded joints (structural steel, engines).

What the calculator does with your input

Third: over-tightening stainless — A2/A4 have 60–70% the strength of class 8.8 steel. Never increase torque to compensate for loosening — replace the fastener.

Second: ignoring property class — 4.6 and 12.9 need very different torque at the same diameter. For critical joints use a torque wrench with ±4% accuracy. Most common: using one torque amount for dry and lubricated joints (25% error).

Re-check torque after 24 hours (preload drops 5–10% on first loading).

One sentence less, one worked example more:

The traps to sidestep

Respect the torque, pick the right class, log the batch — that's the difference between a joint that holds for 20 years and one that fails on first vibration. Steel: 4.6, 5.6, 8.8, 10.9, 12.9. How this calculation applies in Canada: Keep the original measurement, invoice, specification or log beside the calculation so that a misplaced decimal point can be found.

What to keep in mind

It builds on ISO 898 and DIN 933/931 plus the classic T = K × D × F expression (T — torque in Nm, K — friction coefficient 0.15–0.20, D — nominal diameter in m, F — preload in N). Fasteners look simple but are critical on load-bearing assemblies.

Canada mixes metric measurement with imperial habits, so Bolt torque calculator is configure to match what people really quote here. Recalculate after changing one input at a time; this gives which assumption controls the calculated value and makes an unexpected answer easier to diagnose.

Situations this was built for

• Local notes: Amounts on this page use Canadian dollars and metric units, with provincial variation noted where it matters.
• Units of quantify: Officially metric (km, kg, °C, L) but Imperial holdovers persist: heights in feet/inches, weights in pounds, oven temperatures regularly °F. Grocery pricing generally per 100 g.
• Currency & format: Canadian dollar (CAD, $ or C$). Quebec uses comma as decimal (1 000,00 $), rest of Canada uses period.
• Electrical supply: 120 V / 60 Hz, Type A/B plugs (same as US).
• VAT / sales tax: Canada layers federal GST (5%) with provincial sales tax: HST (13–15%) in ON, NB, NL, NS, PE; separate PST/QST in BC, SK, MB, QC (5–9.975%). Alberta and territories charge only the 5% GST.

Wrapping up

No calculator makes the decision for you. The next step is yours.