Bolt Tightening Torque Calculator

Calculate preload force and recommended tightening torque from diameter, strength class and friction condition (T = K · F · d).

Thread diameter (M)

Strength class (Rp0.2 yield)

Friction condition (K factor)

Preload ratio (% of yield)70 %

50 %90 %

Tensile stress area As (mm²)58.0

Preload force (kN)26.0

Recommended tightening torque (Nm)52

Engineering support for joint calculation

Approximate for coarse-thread metric bolts (example: M10 8.8, K=0.20, 70% → ≈ 52 Nm). Real torque varies with coating, lubrication, washer and surface condition. For safety-critical joints a VDI 2230 calculation and the torque-angle method should be used. The calculation is for information only.

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