mechanical calculator
Bolt Torque Calculator
Find the tightening torque for a bolt from its diameter, target preload, and lubrication condition (K-factor method).
How it works
T = K x D x F, where K is the nut factor (friction), D the bolt diameter, and F the desired preload.
Worked example
1/2 in bolt, 10,000 lb preload, dry (K=0.20): T = 0.20 x 0.5 x 10,000 = 1,000 in-lb = 83.3 ft-lb.
When to use it
- K-factor (nut factor): dry ~0.20, lubricated ~0.15, zinc-plated ~0.18.
- This is the short-form shop method; for critical joints follow the fastener spec.