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Bolt Torque Calculator

Tightening torque from bolt size, grade, lubrication state, and target preload using T = K·F·d. Supports metric coarse (M3 – M64) and imperial UNC (#10 – 1½") bolts. Results in N·m and ft·lb.

Inputs Saved

Common range: 70–80 % of proof load for reusable joints, up to 90 % for one-time (yield) tightening.

Formula. T = K · F · d, where T = torque, K = nut factor (lubrication-dependent), F = bolt preload (axial clamp force), d = nominal bolt diameter. Proof load = Sp · At.

Results

Tightening Torque
T = K · F · d
Target Preload (F)
kN
Proof Load
kN
Tensile Stress Area (At)
mm²
Tensile Strength
MPa

For preliminary use. Real installations should account for joint stiffness, embedment, gasket creep, scatter from K-factor (±25 % typical), thread engagement, and applicable code (e.g. ASME PCC-1, VDI 2230). Critical joints should be verified by torque-and-angle or direct preload measurement.