Nm ↔ lb-ft Torque Converter

The exact conversions

Torque is a force applied at a distance, so every unit is just a force unit multiplied by a length unit. That is all that separates them:

Two shortcuts worth memorising: N·m ÷ 1.356 gets you lb-ft, and lb-ft × 12 gets you inch-pounds. That second one matters more than it sounds — a torque spec of 106 in-lb is not a misprint for 106 lb-ft, it is 8.8 lb-ft, and the difference is a stripped thread in an alloy casting.

Worked the other way: 300 lb-ft is 407 N·m, and 40 kgf·m is 392 N·m — which is 289 lb-ft, not the 40-something the original number might suggest.

lb-ft or ft-lb?

Strictly, torque is pound-foot (lb-ft) — a pound of force acting one foot from the centre — while foot-pound (ft-lb) is a unit of energy, the work done moving a pound through a foot. They are dimensionally identical and the industry uses both spellings for torque interchangeably, including on wrenches and in workshop manuals.

So nothing is wrong with your number if the manual says ft-lb and the wrench says lb-ft. Nobody has ever quoted an engine's output in energy units by accident. The distinction only bites in physics homework, and in the one place it genuinely matters: in-lb versus lb-ft on a small torque wrench, where the scales really are twelve times apart.

Why kgf·m keeps showing up

A kilogram-force is the weight of one kilogram under standard gravity — 9.80665 newtons. It is not an SI unit and it has been formally deprecated for decades, but it never went away: Japanese service manuals, older European brochures and a lot of motorcycle literature still quote torque in kgf·m, sometimes written kg·m or m·kg.

The giveaway is the size of the number. A modern turbo four makes something like 40 kgf·m, 400 N·m or 295 lb-ft. If a figure looks implausibly small for an engine — 20, 30, 45 — it is almost certainly kgf·m, and multiplying by 9.80665 puts it back in newton-metres.

Torque figures are quoted at an rpm, and that matters

A torque number on its own is incomplete. "400 N·m" means 400 N·m at some engine speed, and the shape of the curve either side of that point is what you actually feel. This is also where torque and power stop being separate ideas: power is torque multiplied by rotational speed, so the same 400 N·m is worth twice as much power at 6,000 rpm as it is at 3,000.

If you have a torque figure and the rpm it was made at, the torque to hp calculator turns it into horsepower, kilowatts and PS — and shows why every dyno chart crosses at 5,252 rpm.

Crank, wheel and the honest comparison

Two torque figures are only comparable if they were measured at the same place. A manufacturer quotes crank torque on an engine dyno; a rolling road measures wheel torque, which is lower by whatever the drivetrain absorbs — commonly 10–15% on a manual rear-drive car and more on an automatic or an all-wheel-drive system.

Worse, a chassis dyno does not measure engine torque at all. It measures force at the roller and works backwards through the gear ratio, so the "torque" on a rolling-road printout depends on which gear the run was done in. Power is the figure that survives the trip, which is why tuners compare power and enthusiasts argue about torque.

Using this for torque-wrench settings

Converting a workshop figure is the most common reason anyone opens a torque converter, and the arithmetic is the easy part. Three things matter more:

• Stay in the middle of the wrench's range. A click wrench is least accurate in the bottom 20% of its scale — a 30–150 lb-ft wrench set to 35 lb-ft is being asked for its worst work.
• Check whether the spec is dry or lubricated. Oil on the threads can drop the clamp load's relationship to torque by 20–30%, which is enough to yield a bolt that the number said was fine.
• Wind a click wrench back to its lowest setting when you put it away, and have it checked if it has been dropped. A wrench that reads 8% light is worse than no wrench, because you will trust it.

Wheel nuts are the ones people get wrong most often. Typical passenger-car specs run 90–130 N·m (65–95 lb-ft), but the real figure is per-car and per-stud, it is in the handbook, and an impact gun is not a substitute for it.

Conversion charts

Every row below comes from the converter above, driven at build time — the chart and the tool cannot disagree.

Nm to lb-ft

Read across from a newton-metre figure — a European spec sheet or a workshop torque setting — to pound-feet and kilogram-force metres.

lb-ft to Nm

Read across from a pound-foot figure — a US brochure, a dyno sheet or an imperial torque wrench — to newton-metres.

FAQ