Nm to Ft-Lbs Converter

How to convert Nm to ft-lbs

A newton-meter is the torque of a one-newton force pushing on a lever one meter long. A foot-pound (more strictly a pound-foot, lbf·ft) is one pound-force on a one-foot lever. Both pieces of the imperial unit are fixed in SI terms: a foot is exactly 0.3048 m, and a pound-force is the weight of 0.45359237 kg under standard gravity of 9.80665 m/s², which is 4.4482216153 N. Multiply the two and one ft-lb comes to 1.3558179483 N·m. Dividing a newton-meter figure by that number gives foot-pounds; the ft-lbs to Nm converter multiplies by it instead, and the torque converter adds in-lbs, kgf·m and kgf·cm.

Two traps catch people. First, the “pound” in a torque spec is pound-force, not the pound on a kitchen scale; the newtons to pounds converter shows the force relationship on its own. Second, an inch-pound is twelve times smaller than a foot-pound, so small specs are often printed in in-lbs instead. If your spec is under about 15 N·m, check which scale your wrench uses, or use the Nm to in-lbs converter.

Step by step

1. Take the torque spec in newton-meters (N·m or Nm).
2. Divide it by 1.3558179483, or multiply by 0.7375621.
3. Round to your torque wrench's graduation, usually the nearest whole ft-lb.

See it on a scale

How do you set a ft-lb torque wrench to a Nm spec?

Divide the N·m figure by 1.3558 and set the nearest graduation on the ft-lb scale, so a 120 N·m spec becomes 88.51 ft-lbs and you set 89. Most modern service manuals, bike components and European or Japanese cars list torque in N·m, while many American click wrenches are scaled only in ft-lbs. A few habits make the result trustworthy:

1. Convert the original N·m figure, not a rounded ft-lb figure someone has already written in the margin.
2. Round to the wrench's smallest graduation, not to a convenient number you happen to remember.
3. Pull smoothly on the handle grip, at a right angle to the wrench, and stop at the first click.
4. Wind a click-type wrench back to its lowest setting before you store it, as most makers recommend, and never use it to break bolts loose.

Specs below about 20% of a wrench's full scale are where accuracy drops, so a 25 N·m spark plug is better done with a smaller 3/8-inch wrench than a big 1/2-inch lug-nut wrench.

How do you convert engine torque from Nm to lb-ft?

Multiply the N·m rating by 0.7376: a small turbocharged four-cylinder rated at 250 N·m makes 184 lb-ft, a 400 N·m engine makes 295 lb-ft and a 700 N·m diesel pickup makes 516 lb-ft. Car makers outside the US quote engine torque in N·m, while American brochures use lb-ft, and the conversion is the same one used for fasteners.

Torque and power are linked by engine speed. In US units, horsepower = lb-ft × rpm ÷ 5,252, which is why torque and horsepower curves always cross at 5,252 rpm. In metric units, kW = N·m × rpm ÷ 9,549. So 400 N·m at 5,000 rpm is 209.4 kW, or 280.9 hp. The kW to hp converter switches between the two power ratings.

How can I convert Nm to ft-lbs in my head?

Take three quarters of the N·m figure and knock off about 2%: 80 N·m × 0.75 = 60, and the exact answer is 59.0 ft-lbs. When your hands are greasy and the phone is across the room, three shortcuts get you close enough to pick a setting:

• Take three quarters. Multiplying by 0.75 is only about 1.7% high. 80 N·m × 0.75 = 60 ft-lbs, against an exact 59 ft-lbs.
• Use 0.74 for near-exact results. 0.74 is within 0.33% of the true factor, so 140 N·m × 0.74 = 103.6 ft-lbs versus 103.26 ft-lbs.
• Remember the anchors. 10 N·m ≈ 7.4 ft-lbs, 50 N·m ≈ 36.9 ft-lbs and 100 N·m ≈ 73.8 ft-lbs. Scale from whichever is closest.

For the final setting on the wrench, use the exact converter above; the shortcuts are for checking a figure, not for tightening a wheel.

What are the most common Nm to ft-lbs mistakes?

The usual errors are multiplying instead of dividing, reading the wrong scale on a dual-scale wrench, mistaking kgf·m for N·m and ignoring whether the spec assumes dry or lubricated threads.

• Multiplying instead of dividing. The ft-lb number is always the smaller one. If 50 N·m turns into 68, you went the wrong way: the right answer is 36.88 ft-lbs.
• Reading the wrong scale. Dual-scale wrenches print N·m and ft-lbs side by side. Setting 30 on the N·m scale when you meant 30 ft-lbs leaves the bolt about 26% under-tightened.
• Mixing in kgf·m. Older Japanese manuals give torque in kilogram-force meters. One kgf·m is exactly 9.80665 N·m, or 7.233 ft-lbs, so a 10 kgf·m spec is about 72.3 ft-lbs.
• Ignoring lubrication. Oil, anti-seize or threadlocker changes how much clamping force a given torque produces. Use the dry or lubricated figure exactly as the manufacturer specifies.