When to use it
Use it for preliminary estimates, training, and sensitivity checks when clamp force, nominal diameter, and a defensible nut factor are known. Prefer the OEM, engineering drawing, or controlled bolting procedure for real assembly work.
Bolt Torque Calculator
Estimate tightening torque from clamp force, diameter, and K factor.
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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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All calculations run locally in your browser. Nothing you type is sent to a Dockzio server.
Practical guidance
Estimate torque only after defining the joint assumptions
Torque is an indirect way to target bolt preload. Most applied torque is consumed by thread and bearing friction, which is why the nut factor has such a large effect on the result.
Worked example
For a 1/2 in bolt, 10,000 lbf target preload, and K = 0.20, T = K × F × D gives 1,000 lbf·in, or about 83.3 lbf·ft. Changing K to 0.15 lowers the calculated torque to 62.5 lbf·ft while targeting the same preload.
Inputs and interpretation
F is desired clamp force, D is nominal bolt diameter, and K is the assumed nut factor for the exact lubrication, coating, washer, thread, and reuse condition. The output is an estimated tightening torque—not a measured preload or proof that the joint is adequate.
Limits and safety
Real torque-preload scatter can be large, and the short-form equation does not check proof load, thread engagement, joint stiffness, gasket relaxation, fatigue, or tightening sequence. Safety-critical and pressure-boundary joints require validated specifications and calibrated procedures.
FAQ
Quick answers to common questions.
It lumps together thread and bearing-surface friction into a single number used in T = K x F x D. It is not a fixed material property — it changes with lubrication, plating, and surface condition, and published values can vary by ±25–35% for a given "condition".
It is a widely used approximation, not a precise measurement. For safety-critical or structural fasteners, always use the manufacturer's or engineering drawing's specified torque instead.
Yes. Toggling the unit system converts your clamp force and diameter so the underlying physical values stay the same.
No. All calculations run locally in your browser. Nothing you enter is sent to a Dockzio server.
Learning Center
Guides related to Bolt Torque Calculator
Short explainers that pair well with this tool — concepts first, then practice.
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