Foot-pounds and newton-metres both measure torque — a twisting force — and converting between them is straightforward. The confusion comes from the name: a “foot-pound” is also used as a unit of energy, and the two are not interchangeable. This guide covers the conversion, a table for the values that come up on torque wrenches, and how to avoid the unit trap.
The conversion
1 ft-lb = 1.355818 Nm and 1 Nm = 0.737562 ft-lb
So: Nm = ft-lb × 1.3558 and ft-lb = Nm × 0.7376. For quick mental work, multiply ft-lb by about 1.36, or divide Nm by about 1.36 to go back.
Worked example: a service manual specifies 80 ft-lb for a wheel lug nut. In newton-metres that is 80 × 1.355818 = 108.5 Nm. Most European manuals would round this to 110 Nm — a 1.4% difference that is well inside the tolerance of a torque wrench.
Going the other way, a spec of 25 Nm is 25 × 0.737562 = 18.4 ft-lb.
Common torque values
| ft-lb | Nm | Typical application |
|---|---|---|
| 5 | 6.8 | Small electronics / bicycle accessory bolt |
| 10 | 13.6 | Bicycle stem bolt |
| 20 | 27.1 | Small engine bolt, M8 fastener |
| 30 | 40.7 | Brake caliper bolt |
| 50 | 67.8 | Suspension component |
| 80 | 108.5 | Passenger car lug nut |
| 100 | 135.6 | Truck lug nut |
| 150 | 203.4 | Heavy suspension, axle nut |
| 250 | 338.9 | Crankshaft pulley bolt |
| 450 | 610.1 | Heavy equipment wheel bolt |
The Torque Converter converts between ft-lb, Nm, inch-pounds and kgf·m if you need values outside this table.
The trap: torque versus energy
A “foot-pound” is used for two different quantities, and they are not the same thing:
- Torque (lb·ft or ft-lb): a twisting force. 1 ft-lb = 1.3558 Nm.
- Energy / work (ft·lbf): the work done by a force over a distance. 1 ft·lbf = 1.3558 joules.
Notice the conversion factor is numerically identical — 1.3558 — but the target unit is different: newton-metres for torque, joules for energy. A muzzle energy figure quoted in “foot-pounds” is energy, and converting it to “Nm” would be wrong; it should become joules. In practice, torque is almost always written lb-ft or ft-lb in a mechanical manual, and energy figures come from ballistics, engines and physics problems. Check which world you are in before converting.
Practical notes for torque wrenches
Torque specs assume dry, clean threads unless the manual says otherwise. Lubricated threads can deliver substantially more clamping force at the same indicated torque, which is a common cause of stretched or snapped bolts. If a spec calls for lubricated or “wet” torque, it will usually be noticeably lower than the dry figure.
Torque wrenches are least accurate at the ends of their range. A wrench rated 20–150 ft-lb is most trustworthy in the middle; tightening a 10 ft-lb bolt with it is asking for error. Use a smaller wrench or an inch-pound wrench for low values. And always store a click-type wrench wound back to its lowest setting, or the spring will drift out of calibration.
Inch-pounds: the small end of the scale
Below about 20 ft-lb, most US tools and specs switch to inch-pounds (in-lb), because the numbers become easier to read. The relationship is exact: 1 ft-lb = 12 in-lb, since the only change is feet to inches.
To convert in-lb to Nm directly: 1 in-lb = 0.112985 Nm. So a spec of 100 in-lb is 11.3 Nm, and 100 in-lb is also 8.33 ft-lb. Working through ft-lb first (divide by 12, then multiply by 1.3558) gives the same answer and is often less error-prone if you already have the ft-lb factor memorised.
| in-lb | ft-lb | Nm |
|---|---|---|
| 12 | 1.0 | 1.36 |
| 24 | 2.0 | 2.71 |
| 60 | 5.0 | 6.78 |
| 120 | 10.0 | 13.56 |
| 240 | 20.0 | 27.12 |
This is the range where carbon-fibre parts, bicycle components and small engine covers live, and where over-torque does real damage. A dedicated inch-pound wrench is worth having if you work there regularly, because a ft-lb wrench is imprecise at the bottom of its range.
Key Takeaways
1 ft-lb = 1.355818 Nm and 1 Nm = 0.737562 ft-lb; multiply ft-lb by about 1.36 for quick work. An 80 ft-lb lug nut is 108.5 Nm. Watch the distinction between torque (converts to Nm) and energy (converts to joules), and match your torque wrench to the range you are actually working in.