Bolt tightening torque, without the unit juggling

Estimate tightening torque from nominal bolt diameter, target preload, and nut factor. Switch between metric and imperial without re-entering the problem.

What K means: the nut factor represents thread and bearing-surface friction. A commonly used starting assumption is 0.2 for a plain, unlubricated fastener, but coatings, lubrication, finish, and joint geometry can change the required torque substantially.

What this estimate does—and does not—tell you

The preload method uses T = K × F × d: tightening torque equals nut factor times target preload times nominal diameter. The unit conversion is exact; the engineering uncertainty is in the nut factor and the preload you choose.

This is a first-pass estimate, not a substitute for the fastener manufacturer's data, a qualified bolted-joint analysis, or a controlled torque-tension test. Verify the fastener grade, proof load, lubrication condition, thread engagement, joint stiffness, and governing standard before releasing a value to production.