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Torque Converter
Convert newton-metres, pound-feet and kilogram-force metres for wrenches and specs.
If you searched this expecting your car’s automatic gearbox, this is a different thing — that torque converter is a fluid coupling. This one converts units of twisting force, the number stamped on every torque wrench and every wheel-nut spec sheet.
Why wheel-nut torque is not a suggestion
Torque measures a twisting force at a distance from a pivot — how hard you are turning a nut, multiplied by the length of the lever doing the turning. A typical passenger car wheel nut needs somewhere between 100 and 140 N·m, depending on the vehicle, and both directions of getting it wrong cause real problems.
Under-tighten and the wheel can work loose over hundreds of miles of vibration. Over-tighten and you can warp a brake disc, stretch or snap a wheel stud, or strip the threads entirely — none of which show up as an immediate problem, which is exactly why torque wrenches exist instead of “tight enough by feel.”
Torque units compared
| Unit | In N·m | In lb-ft | In kgf·m |
|---|---|---|---|
| 1 N·m | 1 | 0.738 | 0.102 |
| 1 lb-ft | 1.356 | 1 | 0.138 |
| 1 kgf·m | 9.807 | 7.233 | 1 |
Industries where the exact figure matters
- Automotive: wheel nuts, cylinder head bolts, and suspension components all carry specific torque figures in a workshop manual.
- Aerospace: fastener torque on an aircraft is checked and logged, because a loose or over-torqued bolt can be a structural failure waiting to happen.
- Cycling: carbon-fibre components, especially handlebar stems and seatposts, often carry torque limits as low as 4–6 N·m — a fraction of a car spec, and easy to exceed by hand.
- Furniture and flat-pack assembly manufacturers increasingly print torque figures for structural bolts, not just “tighten firmly.”
The easiest mistake: N·m confused with lb-in, not lb-ft
Small fasteners are often specified in pound-inches (lb-in) rather than pound-feet, and the two are easy to mix up because they share the word “pound.” There are 12 lb-in in every lb-ft, so misreading a 20 lb-in spec as 20 lb-ft overtightens a small bolt by a factor of twelve — more than enough to snap it. The same kind of imperial-versus-metric mismatch, on a much larger scale, was blamed for the loss of NASA’s Mars Climate Orbiter in 1999, when ground software produced thruster data in pound-force seconds instead of the newton-seconds the navigation team expected.
Torque conversion questions
How do I convert newton-metres to pound-feet?
Multiply by 0.738. So a wheel-nut spec of 120 N·m converts to about 88.6 lb-ft, a figure you would set directly on an imperial torque wrench.
What torque should car wheel nuts be set to?
It varies by vehicle, typically somewhere between 100 and 140 N·m, and the correct figure is always in the owner’s manual. Never guess or rely on a generic figure, since it depends on stud size and material.
What is the difference between lb-ft and lb-in?
Both measure torque in pounds and a length, but lb-ft uses feet and lb-in uses inches, and there are 12 lb-in per lb-ft. Confusing the two is a common and damaging mistake on small fasteners specified in lb-in.
What is kgf·m and where is it used?
Kilogram-force metres, an older metric unit still seen on some Asian-market vehicle manuals and older tools. 1 kgf·m equals 9.807 N·m, since it is defined using standard gravity rather than being a pure SI unit.
Why does over-tightening a bolt weaken it?
Every bolt has a yield point beyond which it stretches permanently rather than springing back. Past that point, clamping force actually drops and the fastener is more likely to fail under load, which is why torque specs have a maximum, not just a minimum.
