Torque-Tension Conversion Calculator

About this calculator

The nut factor (K) method converts a target bolt preload into the wrench torque needed to achieve it, using the relationship T = K × D × F, where T is applied torque, D is the bolt’s nominal diameter, F is the desired clamp force (preload), and K is an empirical nut factor that captures friction under the bolt head, in the threads, and thread geometry — typically around 0.15 to 0.20 for clean, lubricated steel fasteners, but ranging much higher for dry or galled threads.

Mechanical and aerospace engineers, along with assembly technicians on production lines, rely on this conversion because bolted joints depend on preload — not torque itself — to stay clamped together, resist vibration loosening, and provide the fatigue resistance the joint was designed for; torque is simply the easiest quantity to measure and control on the shop floor with a torque wrench.

This calculator takes the bolt diameter, the target preload force, and the nut factor for your fastener condition and returns the tightening torque you need to dial in on the wrench.