Torque Converter
Convert torque between newton-meters, pound-force feet and inches, ounce-force inches, kilogram-force meters and centimeters, and decanewton-meters.
Updated Formula covered by automated tests
Torque specifications are where unit mix-ups turn into stripped threads and loose wheels. A service manual may give a value in newton-meters, the torque wrench in your toolbox may be scaled in pound-force feet, a bicycle component may be printed in N·m while your small driver reads in pound-force inches, and older Japanese and European manuals sometimes use kilogram-force meters. This converter lists a torque in all of those units at once.
It is meant for the moment you are holding a wrench and a spec sheet that disagree: tightening lug nuts, cylinder-head bolts, spark plugs, carbon bike parts, or comparing the torque figures of two engines or electric motors listed in different markets.
The formula
- τ
- Torque, the turning effect of a force about an axis
- F
- Force applied at right angles to the lever, in newtons or pounds-force
- r
- Distance from the axis to where the force is applied, in meters, feet or inches
- N·m
- Newton-meter, the SI unit of torque
Torque is a force multiplied by its lever arm, so every torque unit is a force unit times a length unit. That is why converting between them takes two exact definitions: the pound-force (0.45359237 kg under standard gravity of 9.80665 m/s², giving 4.4482216152605 N) and the foot (0.3048 m) or inch (0.0254 m). One pound-force foot is 12 pound-force inches and 192 ounce-force inches.
You will see both "ft·lb" and "lbf·ft" in print. They mean the same thing on a torque wrench, though some engineers prefer lbf·ft for torque and ft·lbf for energy to keep the two ideas apart. Torque and energy share the same dimensions (force times distance), but torque is not energy: a newton-meter of torque applied through one radian of rotation does one joule of work.
Worked example
Jordan’s owner’s manual gives a wheel-nut torque of 100 lbf·ft, but the only torque wrench available is marked in N·m. Later, a bike stem says 5 N·m and Jordan’s small torque driver reads in lbf·in.
- 1 Multiply by the lbf·ft factor: 100 × 1.3558179 = 135.58 N·m.
- 2 For an old manual in kgf·m, divide by 9.80665: 135.58 ÷ 9.80665 = 13.83 kgf·m.
- 3 For the bike stem, divide by the lbf·in factor: 5 ÷ 0.1129848 = 44.25 lbf·in.
Result: Set the wrench to about 136 N·m for the wheel nuts, and the small driver to about 44 lbf·in for the stem bolts.
Before you rely on the result
- This tool converts units only. Whether a fastener spec applies to dry or lubricated threads, and whether a torque-to-yield bolt needs an added angle, comes from the manufacturer’s instructions.
- Click-type wrenches typically have a stated accuracy of a few percent and are least accurate at the bottom of their range, so pick a wrench whose scale puts the target value near the middle.
Frequently asked questions
How do torque and rpm give horsepower?
Power equals torque times angular speed. In US units, hp = torque (lbf·ft) × rpm ÷ 5252; in SI units, kW = torque (N·m) × rpm ÷ 9549. The constants come from 33,000 ÷ 2π and 60,000 ÷ 2π, which is why horsepower and torque curves cross at 5252 rpm on a US dyno chart.
Is ft·lb the same as lb·ft?
Numerically yes. The order of the units does not change the value, and tool makers use both. The distinction some textbooks draw is only a convention to signal torque (lbf·ft) versus work (ft·lbf).
Does a torque wrench extension change the reading?
A socket extension in line with the drive does not, but a crow’s-foot or adapter that lengthens the lever arm does. Corrected setting = desired torque × L ÷ (L + E), where L is the wrench length and E the added length along the handle.
Why do small fasteners use inch-pounds?
Because the numbers would otherwise be awkward fractions. A 2 N·m spec is 1.48 lbf·ft but 17.7 lbf·in, and small torque drivers are scaled accordingly. Do not set a foot-pound wrench to an inch-pound value: the result would be 12 times too tight.