Bolt Torque Calculator
Clamp load, tightening torque, and proof load for SAE and metric bolts
Results
Tightening Torque
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Clamp Load Fi
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Proof Load
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Formula Reference
Clamp Load: Fi = (Preload% / 100) × Sp × At
Proof Load: Fp = Sp × At
Torque: T = K × Fi × d
where:
Sp = Proof strength (psi or MPa)
At = Tensile stress area (in² or mm²)
K = Nut factor (depends on condition)
d = Nominal bolt diameter (in or m)
K factors: Dry=0.20, Oiled=0.17, Well-lube=0.15,
Zinc=0.17, Cadmium=0.13
Proof Load: Fp = Sp × At
Torque: T = K × Fi × d
where:
Sp = Proof strength (psi or MPa)
At = Tensile stress area (in² or mm²)
K = Nut factor (depends on condition)
d = Nominal bolt diameter (in or m)
K factors: Dry=0.20, Oiled=0.17, Well-lube=0.15,
Zinc=0.17, Cadmium=0.13
Worked Example
1/2″-13 Grade 5 bolt, dry condition (K=0.20), 75% preload.
| Parameter | Value |
|---|---|
| Tensile stress area At | 0.1419 in² |
| Proof strength Sp | 85,000 psi |
| Proof load Fp | 85,000 × 0.1419 = 12,062 lbf |
| Clamp load Fi (75%) | 0.75 × 12,062 = 9,046 lbf |
| Torque T | 0.20 × 9,046 × 0.5 = 905 in-lbf = 75.4 ft-lbf |