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Bolt Torque Calculator
Torque = K × preload × diameter, with preload at 75% of yield.
Typical Dry-Torque Values (K = 0.2)
| Bolt | Grade 8.8 | Grade 10.9 | Grade 12.9 |
|---|---|---|---|
| M6 | 8.6 N·m | 12.6 N·m | 14.7 N·m |
| M8 | 21 N·m | 31 N·m | 36 N·m |
| M10 | 42 N·m | 61 N·m | 72 N·m |
| M12 | 73 N·m | 107 N·m | 125 N·m |
| M16 | 178 N·m | 261 N·m | 305 N·m |
| M20 | 347 N·m | 509 N·m | 596 N·m |
| M24 | 599 N·m | 879 N·m | 1029 N·m |
T = K × F × d | F = 0.75 × σy × As | As = π/4 × (d − 0.9382P)²
FAQ
Does lubrication change torque?
Yes — lubricated bolts need roughly 25–30% less torque for the same preload because K drops from ~0.20 to ~0.14.
Why 75% of yield?
It leaves margin against overtightening while using most of the bolt's capacity. Some critical joints use 90% with calibrated tools.