Bolt Torque to Clamp Force Calculator

Fastener Preload & Clamp Force Estimation

Estimate bolt preload and clamp force from applied torque using this free fastener calculator for UNC and UNF screws.

Bolt Clamp Force Calculator | FalconCAD

Fastener Inputs

Select a fastener and enter torque assumptions. Default values are intended for dry steel fasteners and can be adjusted.

Thread Series

Fastener Size

Applied Torque (in-lb)

Nut Factor / Torque Coefficient K

Typical starting points: dry steel ≈ 0.20, lubricated ≈ 0.15, prevailing torque hardware may be higher.

Fastener Proof Strength (psi)

Target Preload Fraction of Proof Load

Condition Preset

Torque Units

Optional Notes

This field is informational only and does not affect the math.

Basic equation used: T = K × F × D, where T is torque, K is nut factor, F is preload/clamp force, and D is nominal fastener diameter in inches.

Calculated Results

Estimated Clamp Force

1,875 lbf

Estimated Preload as % of Proof Load

62.4%

Suggested Torque at Target Preload

90.0 in-lb

Nominal Diameter0.1900 in

Tensile Stress Area0.0140 in²

Proof Load1,190 lbf

Target Preload893 lbf

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Clamp-force calculations are highly sensitive to friction and lubrication assumptions. Use measured joint testing when preload accuracy is critical.

Reference Notes

Nut factor K is the biggest uncertainty in torque-to-preload estimates.
Proof strength is not the same as yield strength, but it is commonly used when setting target preload.
Stress area is based on Unified thread geometry and is used to estimate proof load.
When joints are torque-critical, lubrication condition, locking features, coatings, and thread fit can significantly affect results.

Typical K Value	Condition
0.20	Dry steel fastener, general starting point
0.15	Lubricated fastener
0.12	Low-friction coated fastener

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