Bolt Torque Calculator

Estimate the tightening torque for a zinc or plain steel SAE bolt, by diameter, grade, and finish. Uses the standard torque–tension equation T = K·D·F.

How It Works

The calculator applies T = K·D·F: K is the nut factor for the surface finish, D the nominal diameter, and F the clamp load. Clamp load is taken as 75% of the grade proof strength times the tensile stress area — the standard assumption for a non-permanent joint. Results are starting values; actual torque varies ±25% with thread condition and lubrication, so confirm critical values against your specification.

Reference values only — always confirm critical fastening decisions against your engineering specification or the fastener manufacturer.

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