Bolt Torque Calculator
Estimate tightening torque from clamp force, diameter, and K factor.
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Everything is calculated in your browser.
Bolt torque inputs
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About the bolt torque calculator
Estimate the tightening torque needed to reach a desired clamp (preload) force using the short-form torque-tension equation T = K × F × D, where K is the nut factor, F is the desired clamp force, and D is the nominal bolt diameter.
How it works
Torque is computed in SI base units (newtons and meters) and converted to your chosen display unit. Switching unit systems preserves the physical clamp force and diameter you entered.
K-factor limitations
The nut factor K lumps together thread friction, bearing-surface friction, and lubrication into a single number. It is not a fundamental material property — the same bolt can have a K factor anywhere from about 0.10 to 0.30+ depending on lubrication, plating, surface finish, and reuse. Published K factors are typical starting points, not guarantees, and can vary by ±25–35% for a given "condition" in practice.
When to use a torque wrench spec instead
For safety-critical, structural, or warranty-governed fasteners, always use the manufacturer's or engineering drawing's specified torque value. This calculator is best for estimating, sanity-checking, or comparing scenarios — not for replacing a validated torque spec.
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FAQ
Quick answers to common questions.