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Bolt tightening torque calculator

Guideline torque and preload for metric bolts by size and grade.

%
≈0.2 plain/dry, ≈0.15 lubricated

Calculating…

How it's calculated

F = proof stress × As × utilisation T = K × F × d

Proof stresses are from ISO 898-1. 8.8 is 580 MPa up to M16 and 600 MPa above; 10.9 is 830 MPa; 12.9 is 970 MPa. Stress areas are for coarse threads.

This is a guideline estimate. Friction varies widely with plating, lubrication and washers. Always use the equipment manufacturer's specified torque where one exists, and engineered values for safety-critical joints.