Bolt Torque & Preload.
Calculate tightening torque for any bolt. Metric M3–M64 and UNC fasteners. Grades 4.6 to 12.9, stainless A2/A4. Adjusts for friction coefficient (dry, lubricated, anti-seize).
Standard ISO metric coarse thread
Friction varies ±25% in practice — torque method is ±25% accurate
TIGHTENING TORQUE
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N·m — apply with calibrated torque wrench
Torque (kgf·m)
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Torque (lb·ft)
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Preload (target)
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Tensile area (As)
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Yield force
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Max breaking force
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As = (π/4) × ((d₂+d₃)/2)²
F_preload = util × σ_yield × As
T = F × (0.16·p + 0.58·d₂·μ + 0.625·d_head·μ)
K-factor: T ≈ K · d · F (where K ≈ 0.20 dry, 0.14 lub.)
F_preload = util × σ_yield × As
T = F × (0.16·p + 0.58·d₂·μ + 0.625·d_head·μ)
K-factor: T ≈ K · d · F (where K ≈ 0.20 dry, 0.14 lub.)
Quick reference — 8.8 grade, μ=0.14, 75% preload
| Bolt | Tensile area (mm²) | Yield force (kN) | Torque (N·m) | Torque (kgf·m) |
|---|---|---|---|---|
| M5 (8.8) | 14.2 | 9.1 | 5.5 | 0.56 |
| M6 (8.8) | 20.1 | 12.9 | 9.5 | 0.97 |
| M8 (8.8) | 36.6 | 23.4 | 23 | 2.34 |
| M10 (8.8) | 58.0 | 37.1 | 46 | 4.69 |
| M12 (8.8) | 84.3 | 53.9 | 80 | 8.16 |
| M14 (8.8) | 115 | 73.6 | 127 | 13.0 |
| M16 (8.8) | 157 | 100 | 197 | 20.1 |
| M20 (8.8) | 245 | 157 | 385 | 39.3 |
| M24 (8.8) | 353 | 226 | 665 | 67.8 |
| M30 (8.8) | 561 | 359 | 1330 | 136 |