🔩 Bolt Torque Calculator
Estimate the tightening torque needed to reach a target clamp force on a bolted joint, based on bolt diameter and friction condition.
What is Bolt Torque?
Bolt torque is the twisting force applied to a fastener during tightening. Applying the right torque helps a bolted joint reach its intended clamp force — too little and the joint can loosen, too much and the bolt can be overstressed.
The Formula
This calculator uses the standard short-form torque equation: T = K × D × F, where T is torque, D is the bolt’s nominal diameter, F is the desired clamp force, and K is a friction (nut factor) coefficient that depends on the bolt’s surface condition and lubrication.
- Dry plain steel: K ≈ 0.20
- Lubricated: K ≈ 0.15
- Stainless steel (dry, higher friction): K ≈ 0.30
Actual K values vary with thread condition, plating, and lubricant brand, so this is a general estimate for planning purposes — for critical or safety-related joints, always follow the fastener manufacturer’s torque specification or a qualified engineer’s calculation.