How it works
The calculation follows the VDI 2230 method: a bolt is correctly tightened when the equivalent stress from tension and torsion reaches 90% of the yield strength. Most of the tightening torque (about 85–90%) is lost to friction in the thread and under the head; only the rest creates preload.
Formula
FM = ν·Rp0.2·As / √(1 + 3·[1.5·d2/d0·(P/(π·d2) + 1.155·μG)]²) MA = FM · (0.16·P + 0.58·d2·μG + μK·Dkm/2)
μ = 0.12 is typical for lightly oiled, zinc-plated or black-oxide bolts; dry stainless surfaces can reach 0.16–0.20, MoS₂ paste 0.08–0.10. The head friction diameter assumes a hex head bolt and a medium clearance hole (ISO 273). Results are a guide; for critical joints the manufacturer’s specification applies.
Chart
| Size | As mm² | 8.8 kN | 8.8 Nm | 10.9 kN | 10.9 Nm | 12.9 kN | 12.9 Nm |
|---|---|---|---|---|---|---|---|
| M3 | 5.0 | 2.5 | 1.4 | 3.7 | 2.0 | 4.4 | 2.3 |
| M4 | 8.8 | 4.4 | 3.1 | 6.5 | 4.6 | 7.6 | 5.3 |
| M5 | 14.2 | 7.2 | 6.1 | 10.6 | 8.9 | 12.4 | 10.5 |
| M6 | 20.1 | 10.2 | 10.5 | 15.0 | 15.4 | 17.5 | 18.0 |
| M8 | 36.6 | 18.6 | 25.3 | 27.4 | 37.2 | 32.0 | 43.6 |
| M10 | 58.0 | 29.6 | 49.7 | 43.5 | 73.0 | 50.9 | 85.4 |
| M12 | 84.3 | 43.1 | 85.4 | 63.3 | 125.4 | 74.1 | 146.8 |
| M14 | 115.4 | 59.1 | 136.0 | 86.9 | 199.7 | 101.7 | 233.7 |
| M16 | 156.7 | 81.0 | 209.6 | 118.9 | 307.8 | 139.2 | 360.2 |
| M18 | 192.5 | 101.9 | 300.6 | 145.1 | 428.1 | 169.8 | 501.0 |
| M20 | 244.8 | 130.5 | 422.6 | 185.8 | 601.9 | 217.5 | 704.3 |
| M22 | 303.4 | 162.6 | 578.4 | 231.5 | 823.8 | 270.9 | 964.1 |
| M24 | 352.5 | 187.9 | 728.0 | 267.6 | 1,036.9 | 313.1 | 1,213.4 |
| M27 | 459.4 | 246.4 | 1,072.9 | 351.0 | 1,528.1 | 410.7 | 1,788.2 |
| M30 | 560.6 | 300.0 | 1,457.7 | 427.2 | 2,076.1 | 499.9 | 2,429.5 |
| M33 | 693.6 | 372.9 | 1,968.3 | 531.1 | 2,803.3 | 621.5 | 3,280.5 |
| M36 | 816.7 | 438.1 | 2,534.4 | 624.0 | 3,609.6 | 730.2 | 4,224.0 |
μG = μK = 0.12, 90% yield utilisation, hex head bolt.
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