Bolt Torque Calculator Formula
Understand the math behind the bolt torque calculator. Each variable explained with a worked example.
Formulas Used
Required Torque
torque_nm = k_factor * f_n * d_mVariables
| Variable | Description | Default |
|---|---|---|
preload | Target Preload Force (F)(kN) | 50 |
bolt_dia | Nominal Bolt Diameter (d)(mm) | 16 |
k_factor | Torque Coefficient (K) | 0.2 |
f_n | Derived value= preload * 1000 | calculated |
d_m | Derived value= bolt_dia / 1000 | calculated |
How It Works
Bolt Torque-Preload Relationship
Torque applied to a bolt creates axial preload that clamps the joint together.
Formula
T = K F d
where T is the tightening torque, K is the nut factor (torque coefficient), F is the desired preload, and d is the nominal bolt diameter. K depends on lubrication: dry steel K = 0.20, lightly oiled K = 0.15, anti-seize compound K = 0.12.
Worked Example
An M16 bolt needs 50 kN preload with K = 0.2 (dry).
preload = 50bolt_dia = 16k_factor = 0.2
- 01F = 50 kN = 50,000 N
- 02d = 16 mm = 0.016 m
- 03T = 0.2 x 50,000 x 0.016 = 160 N-m
Ready to run the numbers?
Open Bolt Torque Calculator