Bolt Torque Calculator

Estimate tightening torque from bolt size, clamp load and friction factor.

Clamp load (preload)

Nominal diameter

K factor

Torque (lb-ft) 41.667

Torque (lb-in) 500

Torque (N·m) 56.492

Formula: T = K × D × F (then ÷ 12 for lb-ft)

Step-by-step with your numbers:

1. Values used:

2. Clamp load (preload) = 5,000

3. Nominal diameter = 0.5

4. K factor = 0.2

6. Torque = 41.667lb-ft

7. Torque = Clamp load (preload) x Nominal diameter x K factor = 5,000 x 0.5 x 0.2 = 500lb-in

8. Torque = 56.492N·m

Did we solve your problem today?

Estimate the torque needed to achieve a target clamp load (preload) on a bolted joint.

The math behind it

T = K × D × F, where T is torque, K is the nut factor (friction), D is nominal diameter, and F is the desired clamp load.

K ≈ 0.20 for plain steel, ~0.15 lubricated, ~0.25 zinc-plated. Result in lb-in; divide by 12 for lb-ft.

5,000 lb preload, 0.5 in bolt, K = 0.2 → T = 0.2 × 0.5 × 5,000 = 500 lb-in = 41.7 lb-ft.

What is the K factor?

An empirical 'nut factor' capturing thread and head friction; lubrication lowers it and reduces required torque.