Torque Converter
Convert newton metres, pound-feet, pound-inches and kilogram-force metres — keeping torque apart from energy, and lb·ft apart from lb·in, which differ by a factor of twelve.
Torque Converter
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- Torque is a vector; this page converts magnitude only and carries no sense of rotation.
- Converting torque to power requires rotational speed, which is outside a unit conversion.
- Fastener specifications depend on thread condition, lubrication and sequence, none of which a converter can capture.
- The pound-foot and foot-pound distinction is a naming convention that not all sources observe.
In short: Torque conversion routes through the newton metre. One pound-foot is exactly 1.3558179483 N·m, the product of the exact pound-force and the exact foot. Two traps: a newton metre is dimensionally a joule but must never be called one, because torque is a vector and energy a scalar; and lb·ft is twelve times lb·in, the commonest fastener-spec error there is.
Formula
Each factor is the number of newton metres in one of that unit. The pound-foot is exact because both of its parts are: the pound-force is exactly 4.4482216152605 N and the international foot is exactly 0.3048 m, so their product is exact to the last digit.
Worked Example
- Identify the source factor. One pound-foot is 1.3558179483 N·m.
- Convert to the SI unit. 100 × 1.3558179483 = 135.58179 N·m.
- Identify the target factor. One newton metre is 1 N·m.
- Divide. 135.58179 ÷ 1 = 135.58179 N·m.
- Check the inch. The same torque is 1,200 lb·in — twelve times the number, not the same one.
The twelve-times error. A carbon bicycle stem bolt specified at 6 N·m is 53.1 lb·in but only 4.43 lb·ft. A torque wrench graduated in pound-feet, set to 53, would apply twelve times the intended torque and crush the steerer. Small fasteners are almost always specified in pound-inches or newton metres precisely because pound-feet are too coarse at that scale — always read which unit is printed on the spec before setting the wrench.
Strengths & Limits Of This Model
Where this engine is strong
- Pound-foot derived as an exact product of exact definitions.
- Reports pound-feet and pound-inches together to expose the twelve-times trap.
- States plainly why the newton metre is not written as a joule.
- Lever-arm readout turns the definition into a usable force.
Where it stops
- Cannot advise a correct torque value for any specific fastener.
- Does not handle torque as a signed vector.
Practical Use Cases
Fastener and assembly specifications
Service manuals mix newton metres, pound-feet and pound-inches, often on the same page. Converting explicitly is the only defence against the twelve-times slip.
Engine and motor ratings
Engine torque appears in N·m in Europe and lb·ft in America, while older Japanese manuals use kgf·m. Pair with the Power Converter when a rating gives power and speed instead of torque.
Bicycle and precision equipment
Carbon components are specified in newton metres at values low enough that pound-feet lose resolution entirely; pound-inches or ounce-inches are the practical imperial units.
Legacy and CGS documentation
Dyne centimetres and poundal feet still appear in older physics and instrumentation literature and need translating into SI.
Methodology & Editorial Standards
All conversions route through the newton metre, the SI derived unit of torque. The pound-foot is computed as the exact product of the pound-force, 4.4482216152605 N by definition since the 1959 international yard and pound agreement combined with the 1901 CGPM standard gravity, and the international foot of exactly 0.3048 m; the pound-inch and ounce-inch follow by exact division by twelve and sixteen. Gravitational metric units use the exact standard gravity of 9.80665 m/s². The engine reports pound-feet and pound-inches simultaneously because the factor of twelve between them is the commonest error in fastener work. The newton metre is deliberately never displayed as a joule: although dimensionally identical, the SI Brochure reserves the joule for energy, and this page states the reason rather than leaving the coincidence to be discovered. All conversion factors are exact by definition under the International System of Units, or exact by international agreement where the unit is defined by treaty. Values are held at full IEEE-754 double precision internally and rounded only for display, so chained conversions do not accumulate drift.
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Torque Converter — 10 Expert FAQs
10 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
How many newton metres are in a pound-foot?
Exactly 1.3558179483314003 N·m. The figure is definitional rather than measured: it is the product of the pound-force, which is exactly 4.4482216152605 newtons, and the international foot, which is exactly 0.3048 metres. Going the other way, one newton metre is 0.7375621493 pound-feet, an irrational decimal because the exact definition runs in the opposite direction.
Is a newton metre the same as a joule?
Dimensionally yes, conceptually no. Both reduce to kg·m²/s², but the SI Brochure reserves the joule for energy and work and keeps the newton metre for torque. Energy is a scalar formed from a dot product; torque is a vector formed from a cross product. Holding a spanner against a tight bolt applies torque indefinitely while doing no work at all.
What is the difference between lb·ft and ft·lb?
Strictly, the pound-foot is the torque unit and the foot-pound is the unit of work or energy. The arithmetic is identical, so the two are constantly used interchangeably in casual writing, but they describe different physical quantities. SAE documentation prefers lb·ft for fastener torque.
Why do lb·ft and lb·in differ by twelve?
Because there are twelve inches in a foot and the lever arm is the part that changes; the force is the same pound-force in both. Small fasteners are specified in pound-inches because pound-feet would give awkward fractions. Confusing the two applies twelve times the intended torque, which is enough to destroy most small components.
What is a kgf·m?
A kilogram-force metre, the gravitational metric torque unit, equal to exactly 9.80665 N·m because it uses standard gravity. It appears throughout older Japanese and European service literature and on some legacy torque wrenches. One kgf·m is about 7.233 lb·ft.
How do I work out the force on a spanner?
Divide the torque by the perpendicular distance from the fastener axis to where you push. A 100 N·m torque on a 0.3 m spanner needs about 333 newtons, roughly 75 pounds of force. Double the spanner length and you halve the force needed for the same torque, which is why breaker bars work.
Can I convert torque to horsepower?
Not directly — you also need rotational speed, because power is torque multiplied by angular velocity. Torque alone says how hard something twists; power says how fast it can do work. An engine's peak torque and peak power almost never occur at the same speed.
Why is torque sometimes written as joules per radian?
Because multiplying a torque by an angle in radians gives energy. Since the radian is dimensionless, joules per radian reduces to joules dimensionally, but the notation makes clear that torque only becomes work once rotation happens. It is a useful reminder rather than a standard unit.
What is an ounce-inch used for?
Very small torques, chiefly in model servos, small electric motors and precision instruments. One ounce-inch is a sixteenth of a pound-inch, about 7.06 mN·m. A typical hobby servo rated 400 oz·in produces about 2.82 N·m.
Does the direction of torque matter for conversion?
Not for the unit conversion itself, which handles magnitude only. But torque is a vector with a sense of rotation, clockwise or anticlockwise, and that sign matters in any calculation that sums torques about an axis. This converter treats the value as a magnitude.