Bolt Torque Calculator
Use this bolt torque calculator to estimate tightening torque from the bolt type, torque coefficient K, lubrication factor, bolt diameter, and target clamping force.
Tightening Torque
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Quick Answer: Omni's relation is torque = K x F x d x (1 - lubrication factor / 100), where K depends on bolt condition and the lubrication factor reduces the dry-torque estimate.
How to Calculate
- Choose the bolt type: Pick one of Omni's preset bolt conditions or enter a custom torque coefficient K.
- Choose lubrication: Select the lubricant state or enter a custom lubrication factor.
- Enter diameter and clamping force: Use consistent units for force and length.
- Review the torque result: The calculator returns the tightening torque based on the selected coefficient and lubrication adjustment.
Formula
T = K x F x d x (1 - l / 100)
| Variable | Meaning | Unit |
|---|---|---|
| T | Tightening torque | force x length |
| K | Torque coefficient for the bolt condition | dimensionless |
| F | Target clamping force | force |
| d | Bolt diameter | length |
Worked Examples
Fastener tightening - Zinc-plated mild-steel bolt with oil
- Bolt type: Mild-steel, zinc-plated
- Lubricant: SAE 30 oil
- Diameter: 0.75 in
- Clamping force: 25,000 lb
Result: Use the formula T = K x F x d x (1 - l / 100) with K = 0.20 and l = 40
The lubrication adjustment reduces the dry torque estimate compared with an unlubricated condition.
Interpretation Table
| Range | Meaning | Action |
|---|---|---|
| Lower torque | Lower clamping force, smaller diameter, or more lubrication | Confirm the final value against the bolt specification or standard torque chart. |
| Higher torque | Higher clamping force, larger diameter, or higher dry-friction coefficient | Check thread condition, grade, and the joint material before tightening. |
| Custom K or l | Project-specific friction assumptions | Document the source of the coefficient and lubrication factor for traceability. |
Frequently Asked Questions
Omni presents the torque equation as T = K x F x d x (1 - l / 100).
K is a factor that captures the combined friction behavior of the threads and bearing surfaces for the chosen bolt condition.
Lubrication reduces friction, which changes the torque needed to achieve a given clamping force.
Note: This calculator is for estimation and training. Critical joints should use the manufacturer's tightening procedure, applicable standards, and calibrated tools.
References
Last reviewed: March 14, 2026