Bolt Pretension and Torque Calculator

Estimate tightening torque from bolt diameter, target preload, and nut factor with clear unit handling and practical warnings.

Calculator

Bolt pretension and torque estimate

Nominal bolt diametermmTarget preloadkNNut factorK

Tightening torque480 N-m

Tightening torque354 lbf-ft

Target preload120,000 N

Torque per kN preload4 N-m/kN

T = K x F x d

F in newtons, d in metres, T in newton metres.

Confirm the nut factor, lubrication, thread condition, and project requirements before applying results.

Enter bolt size, grade, friction factor, and target preload.

Estimate tightening torque with clearly stated assumptions.

Compare results across common friction conditions.

Review warnings before using values for design decisions.

The estimate uses the simplified torque relationship T = K x F x d.

Nut factor represents the combined effect of thread and bearing friction.

The result is an engineering estimate, not a substitute for project-specific bolting procedure validation.

Does not calculate bolt stress area, proof load, embedment loss, relaxation, gasket behavior, or tightening scatter.

Does not replace flange, pressure boundary, structural, or safety-critical design review.

T is tightening torque, K is nut factor, F is target preload, and d is nominal bolt diameter.

The calculator converts preload from kN to N and diameter from mm to m before calculating N-m.