ft-lbs, N·m and kgf·m: torque units
Torque is force times lever arm. The SI unit is the newton-meter (N·m); US wrenches and manuals use pound-feet (lbf·ft, usually written "ft-lbs"). Because the pound and the foot are defined exactly, 1 lbf·ft = 0.3048 m × 4.4482216 N = 1.3558179 N·m.
- lbf·ft (ft-lbs): lug nuts, engine and suspension bolts, engine torque ratings.
- lbf·in (in-lbs): small fasteners, bicycles, electrical terminals; 12 in-lbs = 1 ft-lb.
- N·m: European and Asian service manuals; most torque wrenches show both scales.
- kgf·m: older Japanese and Latin American specs; 1 kgf·m = 9.80665 N·m. Hobby servos are often rated in kgf·cm.
1 lbf·ft = 1.3558179483 N·m 1 N·m = 0.737562 lbf·ft
1 lbf·in = 0.1129848 N·m 1 N·m = 8.85075 lbf·in
1 kgf·m = 9.80665 N·m = 7.23301 lbf·ft
ft-lbs to N·m and kgf·m table
| lbf·ft | N·m | kgf·m |
|---|---|---|
| 10 lbf·ft | 13.558 | 1.3825 |
| 15 lbf·ft | 20.337 | 2.0738 |
| 20 lbf·ft | 27.116 | 2.7651 |
| 25 lbf·ft | 33.895 | 3.4564 |
| 30 lbf·ft | 40.675 | 4.1476 |
| 40 lbf·ft | 54.233 | 5.5302 |
| 50 lbf·ft | 67.791 | 6.9127 |
| 60 lbf·ft | 81.349 | 8.2953 |
| 75 lbf·ft | 101.69 | 10.369 |
| 80 lbf·ft | 108.47 | 11.06 |
| 90 lbf·ft | 122.02 | 12.443 |
| 100 lbf·ft | 135.58 | 13.825 |
| 120 lbf·ft | 162.7 | 16.591 |
| 150 lbf·ft | 203.37 | 20.738 |
| 200 lbf·ft | 271.16 | 27.651 |
| 250 lbf·ft | 338.95 | 34.564 |
| 300 lbf·ft | 406.75 | 41.476 |
Worked example: lug nuts
Many passenger cars specify somewhere around 75–100 ft-lbs for the lug nuts (always use the figure in your owner's manual). At 80 ft-lbs: 80 × 1.35582 = 108.47 N·m, so set a metric wrench to about 108 N·m. A 30 in-lb spec is 3.39 N·m, not 30 N·m.
Frequently asked questions
How many N·m is 1 ft-lb?
1 lbf·ft = 1.35582 N·m; 1 N·m = 0.737562 ft-lbs.
How do I convert in-lbs to ft-lbs?
Divide by 12: 120 in-lbs = 10 ft-lbs = 13.56 N·m.
What is 100 N·m in ft-lbs?
100 N·m = 73.756 ft-lbs.