M18 Bolt Torque
An M18 8.8 bolt with a coarse M18×2.5 thread needs about 303.5 N·m (223.9 ft·lb) when dry and 227.1 N·m (167.5 ft·lb) when oiled, tightened to 70% of yield (clamp force 86.2 kN).
| Grade | Clamp forcepreload | Dryμ 0.15 | Oiledμ 0.11 | PTFE / moly pasteμ 0.06 |
|---|---|---|---|---|
| 4.6 | 32.3 kN7269 lbf | 113.8 N·m84.0 ft·lb | 85.2 N·m62.8 ft·lb | 56.5 N·m41.7 ft·lb |
| 4.8 | 43.1 kN9692 lbf | 151.8 N·m111.9 ft·lb | 113.6 N·m83.8 ft·lb | 75.3 N·m55.6 ft·lb |
| 5.6 | 40.4 kN9087 lbf | 142.3 N·m104.9 ft·lb | 106.5 N·m78.5 ft·lb | 70.6 N·m52.1 ft·lb |
| 5.8 | 53.9 kN12115 lbf | 189.7 N·m139.9 ft·lb | 141.9 N·m104.7 ft·lb | 94.2 N·m69.5 ft·lb |
| 6.8 | 64.7 kN14539 lbf | 227.7 N·m167.9 ft·lb | 170.3 N·m125.6 ft·lb | 113.0 N·m83.3 ft·lb |
| 8.8 | 86.2 kN19385 lbf | 303.5 N·m223.9 ft·lb | 227.1 N·m167.5 ft·lb | 150.7 N·m111.1 ft·lb |
| 10.9 | 121.3 kN27260 lbf | 426.9 N·m314.8 ft·lb | 319.4 N·m235.6 ft·lb | 211.9 N·m156.3 ft·lb |
| 12.9 | 145.5 kN32712 lbf | 512.2 N·m377.8 ft·lb | 383.3 N·m282.7 ft·lb | 254.3 N·m187.5 ft·lb |
| A2-70 | 60.6 kN13630 lbf | 213.4 N·m157.4 ft·lb | 159.7 N·m117.8 ft·lb | 105.9 N·m78.1 ft·lb |
| A4-70 | 60.6 kN13630 lbf | 213.4 N·m157.4 ft·lb | 159.7 N·m117.8 ft·lb | 105.9 N·m78.1 ft·lb |
| A4-80 | 80.8 kN18173 lbf | 284.6 N·m209.9 ft·lb | 212.9 N·m157.0 ft·lb | 141.3 N·m104.2 ft·lb |
| Grade | Clamp forcepreload | Dryμ 0.15 | Oiledμ 0.11 | PTFE / moly pasteμ 0.06 |
|---|---|---|---|---|
| 4.6 | 36.3 kN8167 lbf | 124.1 N·m91.5 ft·lb | 91.3 N·m67.3 ft·lb | 58.5 N·m43.2 ft·lb |
| 4.8 | 48.4 kN10889 lbf | 165.4 N·m122.0 ft·lb | 121.7 N·m89.8 ft·lb | 78.0 N·m57.6 ft·lb |
| 5.6 | 45.4 kN10208 lbf | 155.1 N·m114.4 ft·lb | 114.1 N·m84.2 ft·lb | 73.2 N·m54.0 ft·lb |
| 5.8 | 60.5 kN13611 lbf | 206.8 N·m152.5 ft·lb | 152.2 N·m112.2 ft·lb | 97.6 N·m72.0 ft·lb |
| 6.8 | 72.7 kN16333 lbf | 248.2 N·m183.0 ft·lb | 182.6 N·m134.7 ft·lb | 117.1 N·m86.3 ft·lb |
| 8.8 | 96.9 kN21778 lbf | 330.9 N·m244.0 ft·lb | 243.5 N·m179.6 ft·lb | 156.1 N·m115.1 ft·lb |
| 10.9 | 136.2 kN30625 lbf | 465.3 N·m343.2 ft·lb | 342.4 N·m252.5 ft·lb | 219.5 N·m161.9 ft·lb |
| 12.9 | 163.5 kN36750 lbf | 558.4 N·m411.8 ft·lb | 410.9 N·m303.1 ft·lb | 263.4 N·m194.3 ft·lb |
| A2-70 | 68.1 kN15313 lbf | 232.7 N·m171.6 ft·lb | 171.2 N·m126.3 ft·lb | 109.8 N·m80.9 ft·lb |
| A4-70 | 68.1 kN15313 lbf | 232.7 N·m171.6 ft·lb | 171.2 N·m126.3 ft·lb | 109.8 N·m80.9 ft·lb |
| A4-80 | 90.8 kN20417 lbf | 310.2 N·m228.8 ft·lb | 228.3 N·m168.4 ft·lb | 146.3 N·m107.9 ft·lb |
Torque for M18 hex head bolts and nuts, standard ISO/ASME heads on steel with a 20.0 mm clearance hole. Friction μ applies to both the threads and the bearing face. Always follow the manufacturer's value where one exists.
M18 thread and dimensions
- Coarse thread
- M18×2.5 — pitch 2.5 mm
- Fine thread
- M18×1.5 — pitch 1.5 mm
- Tensile stress area Aₛ
- 192.5 mm² (coarse), 216.2 mm² (fine)
- Pitch diameter d₂
- 16.376 mm
- Tap drill
- 15.5 mm (coarse), 16.5 mm (fine)
- Wrench size (hex head)
- 27 mm
- Clearance hole
- 20.0 mm
How the M18 torque is calculated
Preload is 70% of the bolt's yield strength times its tensile stress area. Torque then follows the ISO 16047 / VDI 2230 formula, which splits it into thread pitch, thread friction and friction under the head:
F = 70% × 640 MPa × 192.5 mm² = 86.2 kN
T = F × (0.16·P + 0.58·μ·d₂ + μ·Dₖₘ/2)
T = 86.2 kN × (0.16·2.5 + 0.58·0.15·16.38 + 0.15·23.50/2) mm = 303.5 N·m
Here d₂ is the pitch diameter and Dₖₘ the effective bearing diameter of the head (23.50 mm). Change the grade, lubrication or preload in the calculator below.
Frequently asked questions
What is the torque for an M18 8.8 bolt?
About 303.5 N·m (223.9 ft·lb) with dry threads, 227.1 N·m (167.5 ft·lb) with oiled threads and 150.7 N·m (111.1 ft·lb) with PTFE or moly paste, for a coarse M18×2.5 thread tightened to 70% of yield. The resulting clamp force is 86.2 kN.
What is the torque for an M18 10.9 bolt?
About 426.9 N·m (314.8 ft·lb) with dry threads, 319.4 N·m (235.6 ft·lb) with oiled threads and 211.9 N·m (156.3 ft·lb) with PTFE or moly paste, for a coarse M18×2.5 thread tightened to 70% of yield. The resulting clamp force is 121.3 kN.
What size wrench fits an M18 bolt?
A standard M18 hex head bolt or nut takes a 27 mm wrench or socket.
What drill size do I need to tap M18?
Use a 15.5 mm drill for M18×2.5 and 16.5 mm for M18×1.5.