Maker Label Studio

Bolt Torque Calculator

Calculate fastener clamp load and tightening torque from nut factor, nominal diameter, proof strength, and target preload.

Cited category: Manufacturing & Materials Formula: T = K x D x F Default preload: 75% of proof load

Inputs

Use a known tensile stress area, or calculate it from a standard thread diameter and pitch.

Unit system
Tensile stress area source

Example: 0.5 for a 1/2 inch bolt.

Unified estimate: 0.7854 x (D - 0.9743 / TPI)^2.

Preset proof strengths are typical values; use Custom for project-specific data.

ksi

K captures thread and bearing friction; verify with your fastener finish and lubricant.

Typical fastener target preload is 75% of proof load.

Reference: Manufacturing & Materials fastener torque uses T = K x D x F, where T is torque, K is nut factor, D is nominal diameter, and F is target clamp load.

Results

Results update as you edit the inputs.

Proof load
Not calculated
Target clamp load
Not calculated
Tightening torque
Not calculated
Tensile stress area
Not calculated
Calculation check
Not calculated

Self-tests

Runs golden test cases against the preload, thread area, and T = K x D x F calculation functions.

Self-tests not run.

About the Bolt Torque Calculator

Bolt torque estimating helps mechanics, fabricators, and engineers translate a target clamp load into tightening torque using nominal diameter and a nut factor. It is useful for preliminary assembly planning and comparison of lubricated versus dry conditions, while recognizing that torque is an indirect method with substantial scatter.

How it works

  1. Enter bolt diameter, thread condition, and target clamp load.
  2. Choose a nut factor that reflects dry, plated, or lubricated conditions.
  3. Select torque units and review the calculated tightening torque.
  4. Compare the result with the joint specification and fastener limits.

Frequently asked questions

What is the basic bolt torque formula?

A common estimating formula is T equals K x D x F, where K is nut factor, D is nominal diameter, and F is target clamp load. It is an approximation, not a direct measurement of tension.

Why does lubrication change torque so much?

Most tightening torque is consumed by thread and bearing friction. Lubrication lowers friction, so the same torque can create much higher clamp load.

How should I choose target clamp load?

Target clamp load is often selected as a percentage of proof load or yield capacity, but the right value depends on joint design, gasket behavior, fatigue, and service conditions.

Is torque control enough for critical bolted joints?

Not always. Critical joints may require tensioning, turn-of-nut, direct tension indicators, ultrasonic measurement, or a written bolting procedure.

Can I reuse the same torque after changing washers or coatings?

No assumption should be made. Washers, coatings, plating, surface finish, and lubricant all change friction and therefore clamp load for a given torque.

References