Bolt Preload (Clamp Load) Calculator

Work backwards from your torque wrench: given the applied torque, diameter, and finish, see the clamp load — and whether the bolt is near yield.

How It Works

This inverts the torque–tension equation T = K·D·F to solve for preload: F = T ÷ (K × D), with torque converted to pound-inches. The bolt stress is then F divided by the tensile stress area, compared against the proof load of the selected grade. Because K varies ±25% with thread condition and lubrication, the result is a starting estimate — a lubricated bolt at the same torque develops far more clamp load (and may yield) than a dry one, which is exactly what the proof-load comparison is for. Always confirm critical joints against the specification.

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

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