Bolt Tightening Torque Calculator
Tightening torque needed to reach a target bolt preload, using the nut-factor method.
Results
Torque
72.00
N·m
Torque
53.10
lbf·ft
What this tool does
The short-form torque equation multiplies the nut factor, the nominal bolt diameter and the preload you want in the joint. It is a planning estimate, not a substitute for the fastener manufacturer's published torque table.
Formula
M = K × d × F
Variables
| Symbol | Meaning | Unit |
|---|---|---|
k | Ratio | — |
d | Diameter | mm |
f | Force | kN |
M | Torque | N·m |
Ml | Torque | lbf·ft |
Worked example
- Ratio0.2
- Diameter12 mm
- Force30 kN
- Torque72.00 N·m
- Torque53.10 lbf·ft
Limitations
- For work that must comply with a standard or be signed off, check the result against the applicable code and have it reviewed by a qualified engineer.
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.
Frequently asked questions
What value of K should I use?
K is the nut factor, and it depends almost entirely on friction. A commonly quoted starting point is 0.20 for plain dry steel bolts, around 0.15 when lightly lubricated and lower still for coated fasteners. Because friction dominates, torque control alone typically scatters preload by ±25 %; where preload really matters, use angle control, bolt elongation measurement or the fastener manufacturer's own figure.