Bolt Tightening Torque Calculator
Calculate the tightening torque for bolts based on bolt size, grade, and lubrication conditions. Enter the bolt size, grade, and lubrication type to get the recommended torque.
0.00 N·m
Recommended Tightening Torque
Clamp Force: 0.00 kN
Target Stress: 0.00 MPa
Target Stress: 0.00 MPa
Bolt Tightening Torque Calculation
This bolt torque tool calculates the correct tightening torque for bolts based on their size, material grade, and lubrication conditions.
Formula:
T = K × F × D
Where:
- T = Torque (N·m or ft·lb)
- K = Nut factor (coefficient of friction)
- F = Clamp force (N or lb)
- D = Nominal bolt diameter (m or ft)
F = 0.75 × (σ × At)
Where:
- σ = Proof stress (MPa)
- At = Tensile stress area (mm²)
- 0.75 = Target 75% of proof load
At = (π / 4) × (d − 0.9382 × p)²
Bolt Grades and Proof Stress:
| Grade | Proof Stress (MPa) | Yield Stress (MPa) | Tensile Stress (MPa) |
|---|---|---|---|
| 4.6 | 240 | 240 | 400 |
| 5.8 | 380 | 400 | 520 |
| 8.8 | 600 | 640 | 800 |
| 10.9 | 830 | 900 | 1040 |
| 12.9 | 970 | 1100 | 1220 |
| A2-70 | 450 | 450 | 700 |
| A4-80 | 600 | 600 | 800 |
Nut Factor (K) by Lubrication:
| Lubrication | Nut Factor (K) |
|---|---|
| Dry | 0.20 |
| Light Oil | 0.18 |
| Grease | 0.16 |
| Moly Disulfide | 0.13 |
| PTFE Coated | 0.12 |
Reference Torque Values
Reference values below are calculated using the same assumptions as the calculator above.
| Bolt Size | Pitch (mm) | Stress Area (mm²) | Torque (N·m) | Torque (ft·lb) |
|---|---|---|---|---|
| M6 | 1.0 | 20.1 | 9.8 | 7.2 |
| M8 | 1.25 | 36.6 | 22.7 | 16.7 |
| M10 | 1.5 | 58.0 | 45.9 | 33.9 |
| M12 | 1.75 | 84.3 | 75.0 | 55.3 |
| M14 | 2.0 | 115.0 | 125.8 | 92.8 |
| M16 | 2.0 | 157.0 | 186.4 | 137.5 |
| M20 | 2.5 | 245.0 | 330.8 | 244.0 |
| M24 | 3.0 | 353.0 | 571.9 | 421.9 |
| M30 | 3.5 | 561.0 | 1136.0 | 838.0 |
| M36 | 4.0 | 817.0 | 1985.3 | 1464.6 |
