Bolt Torque Calculator - Metric (M3 to M30)
Verified by Rachel Mayfield, Supply Chain Analyst - April 2026
This bolt torque calculator gives recommended tightening torques for metric hex bolts from M3 to M30 in property classes 8.8, 10.9, and 12.9. Values are based on ISO 898-1 and VDI 2230 guidelines with a friction coefficient of 0.14 (dry, unlubricated). Adjust the condition selector for lubricated joints.
Select Bolt Size and Property Class
Values based on ISO 898-1 / VDI 2230 with friction coefficient 0.14 (dry). Lubricated joints require lower torque. Always verify against manufacturer specifications for critical applications.
Metric Bolt Torque Reference Table
The full torque reference table below shows recommended values for dry (unlubricated) conditions. For oiled bolts, reduce torque by approximately 25%. For MoS2 or anti-seize paste, reduce by 35%.
| Size | Pitch (mm) | Class 8.8 (Nm) | Class 10.9 (Nm) | Class 12.9 (Nm) |
|---|---|---|---|---|
| M3 | 0.5 | 1.3 | 1.8 | 2.1 |
| M4 | 0.7 | 3.0 | 4.2 | 4.9 |
| M5 | 0.8 | 5.9 | 8.3 | 9.7 |
| M6 | 1.0 | 10.1 | 14.3 | 16.7 |
| M8 | 1.25 | 24.6 | 34.6 | 40.5 |
| M10 | 1.5 | 48.4 | 68.1 | 79.7 |
| M12 | 1.75 | 84 | 118 | 138 |
| M14 | 2.0 | 133 | 188 | 220 |
| M16 | 2.0 | 206 | 290 | 339 |
| M18 | 2.5 | 282 | 397 | 465 |
| M20 | 2.5 | 402 | 566 | 662 |
| M22 | 2.5 | 547 | 770 | 901 |
| M24 | 3.0 | 686 | 966 | 1130 |
| M27 | 3.0 | 1010 | 1420 | 1660 |
| M30 | 3.5 | 1360 | 1910 | 2240 |
How Bolt Torque Works
Bolt torque creates a clamping force (preload) that holds the joint together. The relationship between torque and preload depends on bolt diameter, thread pitch, friction coefficient, and bolt material strength. Property class 8.8 bolts have a minimum tensile strength of 800 MPa. Class 10.9 reaches 1,040 MPa. Class 12.9 reaches 1,220 MPa.
Under-torquing risks joint failure. Over-torquing risks bolt yield or thread stripping. Always use a calibrated torque wrench and follow the manufacturer's specification when one is available.
When to Adjust Torque Values
These values assume standard hex bolts into steel nuts with no washers. Reduce torque for:
- Lubricated threads (oil, grease, or anti-seize) - reduce by 25-35%
- Flanged bolts (larger bearing surface) - reduce by 10%
- Aluminium or brass threads - reduce by 40-50%
- Prevailing torque locknuts (nyloc) - add the prevailing torque to the target
Related Standards
- ISO 898-1 - Mechanical properties of fasteners, bolts, screws, and studs
- VDI 2230 - Systematic calculation of bolted joints
- BS EN ISO 4014 - Hexagon head bolts, product grades A and B
- BS EN ISO 4032 - Hexagon regular nuts, style 1
References
- ISO 898-1:2013 - Mechanical properties of fasteners made of carbon steel and alloy steel
- VDI 2230 Part 1 - Systematic calculation of highly stressed bolted joints
- Companies House - UK supplier verification
Frequently Asked Questions
What torque should I use for an M10 bolt?
An M10 class 8.8 bolt needs 48.4 Nm (dry). Class 10.9 needs 68.1 Nm. Class 12.9 needs 79.7 Nm. Reduce by 25% if lubricated. Values per ISO 898-1 / VDI 2230.
Does lubrication affect bolt torque?
Yes. Lubrication reduces friction and increases preload for the same torque. Lightly oiled bolts need about 25% less torque. Anti-seize paste needs 35% less. Always adjust torque when lubricating.
What is the difference between property class 8.8 and 10.9?
Property class 8.8 has 800 MPa tensile strength and 640 MPa proof load. Class 10.9 has 1,040 MPa tensile and 940 MPa proof load. Class 10.9 is about 40% stronger, used in higher-stress applications like automotive and structural steel.
What is the Bolt Torque Calculator - Metric (M3 to M30) used for?
The Bolt Torque Calculator - Metric (M3 to M30) provides recommended tightening torques for metric hex bolts ranging from M3 to M30, based on property classes 8.8, 10.9, and 12.9 as per ISO 898-1 standards.
How do I select the correct bolt size in the Bolt Torque Calculator - Metric (M3 to M30)?
To choose the right bolt size, simply use the dropdown menu provided by the calculator and select your desired metric size from M3 up to M30. Each option corresponds to a specific torque recommendation based on property class.
Which standards does the Bolt Torque Calculator - Metric (M3 to M30) follow?
The Bolt Torque Calculator - Metric (M3 to M30) adheres to ISO 898-1 and VDI 2230 guidelines, ensuring accurate torque values for dry, unlubricated conditions with a friction coefficient of 0.14.
Can the Bolt Torque Calculator - Metric (M3 to M30) accommodate lubricated joints?
Yes, users can adjust the condition selector within the calculator to account for lubricated joints, which changes the recommended torque values based on different friction coefficients.
Where can UK engineers find suppliers who offer bolts compatible with the Bolt Torque Calculator - Metric (M3 to M30)?
UK engineers can consult local engineering supply catalogs or websites like Fastenal and RS Components, where they will find a range of metric bolts that fit the property classes supported by the calculator.
What are the typical costs associated with obtaining bolts for use with the Bolt Torque Calculator - Metric (M3 to M30)?
The cost of acquiring bolts varies depending on size, quantity, and material. Typically, smaller sizes like M3 or M4 might start at £1 per 100 pieces, while larger bolts such as M27 or M30 could range from £5 to £20 each.
What property classes does the Bolt Torque Calculator - Metric (M3 to M30) include?
The calculator includes property classes 8.8, 10.9, and 12.9 for metric bolts ranging from M3 to M30, providing tailored torque recommendations based on bolt strength and material grade.