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Fastener Calculators

Bolt Torque Calculator

Tightening torque for a bolt from its size, grade and friction condition, with the clamp load.

Enter values

Results update as you type.

Result

Tightening torque

55.68 N·m

Lubrication changes the torque needed by 30% or more — always match the condition to how you will actually assemble it.

In lb·ft
41.07
Clamp load (preload)
27.84 kN
Bolt stress area
58 mm²
Proof load
37.12 kN
Nut factor K used
0.2

Use the manufacturer’s specified torque where one exists — this is a general engineering estimate.

About the Bolt Torque Calculator

Tightening torque is mostly friction: only about 10–15% of the effort actually stretches the bolt. The short-form equation T = K·D·F ties torque to the clamp load through a nut factor that depends on lubrication. Choose your bolt size, grade and condition to get a starting torque and the preload it produces.

Also known as: torque spec calculator, bolt tightening torque, nut torque, clamp load calculator.

How to use this calculator

  1. Enter bolt size, property class, condition, target preload.
  2. The result updates instantly as you type — press Calculate (or Enter) at any time.
  3. Review the breakdown shown under the main result.
  4. Use Copy result or Share to save the answer or send a link with your inputs.

Formula

T = K × D × F (K is the nut factor, F the clamp load)

Worked example

Using the values pre-filled in the calculator above:

  • Bolt size: M10
  • Property class: 8.8 (640 MPa proof)
  • Condition: Dry / as received (K = 0.20)
  • Target preload = 75 % of proof

the calculator returns:

  • Tightening torque: 55.68 N·m
  • In lb·ft: 41.07
  • Clamp load (preload): 27.84 kN
  • Bolt stress area: 58 mm²