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Bolt Torque Calculator

Calculate recommended tightening torque for metric (class 8.8 / 10.9 / 12.9) and SAE imperial (Grade 2 / 5 / 8) bolts. Select bolt size, grade, and lubrication condition — results in both N·m and ft·lbf. No login required.

HOW IT WORKS

Choose a thread standard — Metric (M-series) or Imperial (SAE UNC/UNF).
Select property class or grade — Metric 8.8 / 10.9 / 12.9 or SAE Grade 2 / 5 / 8.
Pick a bolt size and lubrication condition — Dry (K = 0.20), Lubricated (K = 0.15), or Zinc-plated (K = 0.17). Override K for a custom value.
Read torque in N·m and ft·lbf — includes assumed preload (75% of proof load). Export the full chart as CSV.

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Recommended tightening torque for metric (8.8 / 10.9 / 12.9) and SAE imperial (Grade 2 / 5 / 8) bolts based on 75% of proof load.

Property Class

Bolt Size

Lubrication / Nut Factor K

Assumed Preload

16.47 kN

75% of proof load

Target Torque

26.4 N·m

19.4 ft·lbf

⚠ Values are a starting reference based on 75% of proof load with the selected lubrication condition. Always verify against the applicable engineering specification.

Thread	Stress Area (mm²)	Proof Load (MPa)	Preload (kN)	Torque (N·m)	Torque (ft·lbf)
M3	5.03	600	2.26 kN	1.4	1.0
M4	8.78	600	3.95 kN	3.2	2.3
M5	14.2	600	6.39 kN	6.4	4.7
M6	20.1	600	9.04 kN	10.9	8.0
M8	36.6	600	16.47 kN	26.4	19.4
M10	58	600	26.10 kN	52.2	38.5
M12	84.3	600	37.94 kN	91.0	67.2
M14	115	600	51.75 kN	144.9	106.9
M16	157	600	70.65 kN	226.1	166.7
M20	245	580	106.58 kN	426.3	314.4
M24	353	580	153.56 kN	737.1	543.6
M30	561	580	244.03 kN	1464.2	1079.9
M36	817	580	355.39 kN	2558.8	1887.3

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