// Free Engineering Tool

Bolt Torque Calculator

Calculate tightening torque and clamp load for metric bolts to ISO 898-1. Choose bolt size, property class and thread condition, set your target preload, and get torque, preload and bolt stress instantly — plus a full torque table for every size. Uses the T = K·F·d method with verified proof-load data.

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Bolt & Joint

Bolt Size

Property Class

Thread Condition

Target Preload

Nut Factor K

Torque T = K·F·d. Preload F = target% × proof load (As × proof stress, ISO 898-1). K is an approximate lumped friction factor — verify on actual hardware for critical joints.

Results

Tightening Torque — N·m

Clamp Load (Preload) — kN

⚠ Preload exceeds proof load — bolt may yield

Proof Load—

Yield Load—

Stress Area—

Bolt Stress at Preload—

Torque Table — All Sizes at Current Grade & Condition

Size	As (mm²)	Proof (kN)	Preload (kN)	Torque (N·m)

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