Select a metric bolt size and property class to look up the recommended tightening torque from a standard reference table, in Nm and lb-ft.
Recommended Tightening Torque
β
lb-ft β
Full Reference Table (Nm)
Size
8.8
10.9
12.9
M5
7
10
11.7
M6
11.8
17
19.9
M8
28.8
41.3
48.3
M10
57.3
81.8
95.7
M12
99.8
143
167
M16
248
354
413
M20
500
690
809
M24
865
1195
1395
M30
1719
2377
2774
Source: Engineering ToolBox, "Torque Specifications for Metric Bolts" β coarse thread, lightly oiled, ~85% of proof load. M3, M4, M14, M18, M22, M27 are not published in the source table and are omitted here rather than estimated.
β οΈ Actual required torque varies significantly with lubrication, plating/coating, thread condition, and application. Always follow the fastener or equipment manufacturer's specification for safety-critical joints.
Tightening torque is designed to produce the maximum clamping force a bolt can withstand without yielding (permanent deformation). Larger bolt diameters and higher property classes (8.8 < 10.9 < 12.9) can withstand more torque, so their recommended values are higher.
02
This Table's Assumptions
The reference values here assume coarse thread, lightly oiled threads, and tension at roughly 85% of proof load (per Engineering ToolBox and several fastener engineering references citing the same figures). Dry threads, special plating/coatings, or fine-thread variants will change the actual recommended value.
03
Why Are Some Sizes (M3, M4, etc.) Missing?
The standard reference table this calculator cites only publishes the sizes M5 through M30, and does not include authoritative figures for M3, M4, M14, M18, M22, M27. To keep formulas accurate, this calculator does not fabricate unsourced numbers for missing sizes β it only offers sizes present in the source. Consult the bolt or equipment manufacturer's spec sheet for those sizes.
Frequently asked questions
What do property classes 8.8, 10.9, and 12.9 mean?
These are ISO 898-1 bolt property class markings. The first number (8, 10, 12) indicates minimum tensile strength in units of 100 MPa (e.g. "8" = 800 MPa), and the number after the decimal indicates the yield ratio (yield strength / tensile strength, e.g. "8" = 0.8). Higher numbers mean a stronger bolt.
What if I don't have a torque wrench?
Precision-critical work (engines, structures, safety-related parts) should always use a torque wrench. If none is available, use hand-tightening only for temporary assembly, and re-torque to spec with a proper wrench before actual use.
Can I rely on this table exactly as-is?
This table provides general reference values β actual required torque can vary with lubrication, plating, thread condition, and application environment. For automotive, aerospace, structural, or other safety-critical joints, always follow the exact torque specification from the manufacturer.