Torque Units Explained: Newton-metres, Foot-pounds and Inch-pounds

A torque spec is a force and a distance multiplied together — which is why the units look strange until you know what they describe.

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Torque is the twisting effect a force produces about a pivot. It is the quantity stamped on every wheel-nut specification, every engine datasheet and every torque wrench, and it is the reason a long spanner loosens a bolt that a short one will not.

Torque is force times distance

Tighten a bolt with a spanner and two things matter: how hard you push, and how far from the bolt you push. Torque multiplies them:

torque = force × perpendicular distance from the pivot

Push with 20 newtons on a spanner 0.5 metres long and you apply 10 newton-metres. Push equally hard on a spanner twice as long and you get 20 N·m from the same effort. That is the whole idea behind a breaker bar.

Because torque is built from a force unit and a length unit, every torque unit is a pair: newton-metre, foot-pound, inch-pound.

The three units you will actually meet

Newton-metre (N·m) is the SI unit and the base for everything on this site. One newton-metre is one newton applied one metre from the pivot. It is commonly specified on European vehicle and machinery documentation.

Foot-pound (ft·lbf) is one pound-force applied one foot from the pivot. It is frequently encountered in US automotive work. One foot-pound is 1.3558179483314 N·m — a number that comes from multiplying the pound-force (4.4482216152605 N) by the international foot (0.3048 m), both of which are exact definitions.

Inch-pound (in·lbf) is the same idea over one inch instead of one foot. An inch is exactly one twelfth of a foot, so an inch-pound is exactly one twelfth of a foot-pound — approximately 0.1129848290276 N·m. It is used wherever foot-pounds would be awkwardly small: small fasteners, avionics, bicycle components.

A note on naming: some engineering style guides write torque as pound-foot (lbf·ft) and reserve foot-pound for energy, precisely to keep the two apart. Automotive practice and this site both use foot-pound, but if you meet lbf·ft on a datasheet it is the same unit.

You may also see kilogram-force metre (kgf·m), an older metric unit equal to 9.80665 N·m. It survives on legacy Japanese and European equipment.

Convert between them with the newton-metres to foot-pounds and inch-pounds to newton-metres converters, or browse all torque units.

The mistake worth avoiding: torque is not energy

A newton-metre and a joule have identical base dimensions — both are a newton times a metre. They are not the same quantity, and you must never convert between them.

The difference is geometric. Energy is force applied along a distance: push a box one metre and you have done work. Torque is force applied perpendicular to a lever arm: nothing has necessarily moved at all. A bolt held at 100 N·m that is not turning is transferring no energy whatsoever.

This is why the convention exists of writing torque in newton-metres and energy in joules even though the algebra looks the same. If you find a converter that offers newton-metres to joules, it is telling you something physically meaningless. This site keeps torque and energy as separate categories for exactly that reason.

Reading a torque specification

Three details decide whether you hit the number:

Lubrication. A dry-thread and a lubricated-thread spec for the same fastener differ substantially, because oil changes how much of your applied torque becomes clamping force rather than friction. Follow whichever the manual states.

Sequence. On anything with multiple fasteners around a joint — wheels, cylinder heads, flanges — tighten in the specified crossing pattern and in stages. Torquing one bolt fully before its neighbours distorts the joint.

Direction of the reading. A click wrench is calibrated for tightening. Using one to loosen a seized fastener can damage the mechanism.

Worked example

A wheel-nut spec reads 110 N·m and your wrench is graduated in foot-pounds.

  1. Start with the value in newton-metres: 110 N·m.
  2. Divide by the foot-pound factor: 110 ÷ 1.3558179483314.
  3. The result is 81.13 ft·lbf.

Set the wrench to 81 ft·lbf. The 0.13 ft·lbf you dropped by rounding is far smaller than the tolerance of the fastener and well inside the accuracy of the wrench itself — see significant figures and precision for when rounding does and does not matter.

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