How this instrument works
Torque measures rotational force — the twist a spinning shaft delivers, not the straight-line push of a linear force. A newton-metre is what you get when a coherent SI force of one newton acts one metre out from an axis, and it is the unit stamped on European and Japanese engine, motor and pump datasheets: a small utility engine might peak near 50 Nm, a mid-size car engine several hundred, an electric drivetrain more still. Because torque and energy share the same base units, kg·m²/s², engineers keep them apart by convention alone — a shaft delivering steady torque does no work at all until it actually turns.
Foot-pounds measure the identical twist using pound-force and a foot of lever arm instead, and it is what North American dynamometer printouts, outdoor-power-equipment spec sheets and car-buff magazine tables still report. One pound-force is an avoirdupois pound — fixed at 0.45359237 kg since a 1959 international agreement — accelerated at the standard 9.80665 m/s² adopted by the third General Conference on Weights and Measures in 1901; multiplied across a foot of 0.3048 m, that chain settles a pound-force foot at 1.3558179483314004 N·m, a terminating decimal with no experiment behind it anywhere. Flip that ratio and 1 Nm becomes 0.7375621492772654… ft-lb, a fraction that never resolves, so this page carries it to twelve places as 0.737562149277.
Reading a torque figure usually means reading whoever wrote the spec sheet. A German or Japanese small-engine maker states peak torque in newton-metres on a global datasheet; the same figure appears in a North American retail listing or trade magazine converted to foot-pounds, since that is the unit buyers there compare mowers, generators, tillers and outboard motors by. Motorcycle and e-bike manufacturers straddle both conventions depending on their home market, and dynamometer software defaults differ by brand — so a torque curve pulled from a European chassis dyno often needs converting before it sits next to an American one on the same chart.
- Enter your torque reading into the Newton-metres (Nm) field; it opens at 50 Nm, a typical peak-torque figure for a small engine or mid-power electric motor.
- Read the Foot-pounds (ft-lb) field beneath it — it recalculates on every keystroke, no button required.
- Comparing a European spec sheet to an American one? Convert once, then round to the precision the weaker source actually printed.
- Going the other way, from foot-pounds to newton-metres, multiply your ft-lb figure by 1.3558179483314004.
- Plotting a dyno curve? Convert every point individually rather than scaling a chart image — torque curves rarely stay linear enough to eyeball.
Worked example — a 50 Nm motor rating, read in ft-lb
A compact utility engine — the kind fitted to a mid-size generator, pressure washer or walk-behind chipper — carries a manufacturer's datasheet peak of 50 Nm, quoted that way because the engine is designed and rated in Europe. Enter 50 into Newton-metres (Nm) and Foot-pounds (ft-lb) reads 36.8781074639, the figure a North American retailer or reviewer would print on the same spec sheet.
Round that to 36.9 ft-lb for a listing and nothing meaningful is lost — dynamometer repeatability on small air-cooled engines runs a few percent between pulls, far coarser than a tenth of a pound-foot. Multiply 36.8781074639 back by 1.3558179483314004 and it returns 50.000000 Nm to six decimals, confirming the round trip lost nothing but display precision.
Questions
Why do European engine and motor spec sheets use Nm while American ones use ft-lb?
Mostly geography and the standards each industry inherited. Continental European and Japanese manufacturers design to SI from the outset, so a torque curve leaves the engineering department in newton-metres and stays that way through marketing. American outdoor-power-equipment, automotive and small-engine trade publications grew up on imperial dynamometer readouts and pound-force units, and foot-pounds stuck for anything readers compare side by side. Global manufacturers increasingly print both, but a spec sheet with only one figure usually reflects where the document originated, not the machine.
Is this the same Nm used on a fastener torque wrench?
Numerically, yes — a newton-metre of engine torque and a newton-metre of tightening torque convert through the identical 0.737562149277 factor; nothing about the unit changes with what is being twisted. Physically they are very different jobs. A fastener torque spec describes a brief, static clamp-up load applied once with a wrench; an engine or motor rating describes continuous rotating torque delivered at running speed, sustained for as long as the shaft turns. Confusing the two magnitudes matters more than confusing the unit — a 50 Nm engine rating and a 50 Nm bolt spec are unrelated numbers that happen to share dimensions.
Why do torque and horsepower curves cross at 5252 rpm on an American dyno chart?
Because of how imperial horsepower is defined, not by coincidence. One horsepower equals 33,000 foot-pounds of work per minute, and power in foot-pounds per minute equals torque in pound-feet times rpm times 2π. Solve that relationship for the rpm where torque in lb-ft and power in hp are numerically equal and you land on 5252, every time, regardless of engine or motor. Below 5252 rpm a torque curve reads higher than the horsepower curve; above it, horsepower reads higher — a pattern visible on essentially every American dynamometer chart.
Does a higher peak torque number always mean a stronger engine or motor?
Not by itself. Peak torque tells you the hardest twist a shaft delivers at one particular speed, but usable output depends on power — torque multiplied by how fast the shaft is spinning — and on where in the rev range that peak sits. A small, high-revving motor can out-accelerate a torquier but slower-spinning one because it delivers more power overall, even with a lower peak-torque number on its spec sheet. Torque figures compare most usefully across machines of a similar type and speed range, not across radically different designs.
How do electric motor torque ratings differ from combustion engine ratings?
Differently, in an important way. A combustion engine's torque rises from idle to a peak partway through its rev range then falls off near redline, so its spec sheet quotes that one peak figure alongside the rpm it occurs at. An electric motor typically delivers close to its maximum torque from a standstill, holding it flat until a base speed where power limiting takes over — which is why an electric drivetrain can feel stronger off the line than its torque number implies. Motor datasheets also often split peak (short-burst) torque from continuous (sustained) torque, a distinction combustion-engine sheets rarely spell out.
How many decimal places actually matter when comparing spec sheets?
One decimal place, generally, and often none. Small-engine dynamometer readings vary a few percent pull to pull depending on ambient conditions, fuel and the engine's own tolerances, so a converted figure like 36.8781074639 ft-lb is honestly 36.9 give or take a percent or two. Full precision is worth keeping only while chaining conversions or recreating a chart from tabulated data, so an intermediate rounding error does not compound; round once, at the very last step, to whatever precision the original spec sheet actually supports.
How is this different from the site's other Nm and foot-pound calculators?
The arithmetic is identical — this page and the site's dedicated fastener-torque Nm-to-ft-lb converter both apply the same 0.737562149277 factor, since a newton-metre converts to a foot-pound the same way no matter what's being twisted. They serve different jobs: this page centers on continuous engine and motor torque — spec sheets, dyno curves, peak-torque ratings — while the fastener-focused converter targets one-time bolt tightening under ISO 6789 wrench tolerances. Working in inch-pounds instead of foot-pounds? The site's separate Nm-to-in-lb and in-lb-to-Nm converters apply that factor directly, instead of making you multiply this page's result by 12.