Torque Unit Converter (Nm, lb-ft)
Convert torque between Nm, lb-ft, lb-in, kgf·m and Ncm — all values update at once.
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How It Works
Torque measures a twisting force: the product of a force and the length of the lever arm it acts through (torque = force × distance), which is why its units are always a force unit times a length unit — newton-metres (Nm), pound-force-feet (lb-ft), pound-force-inches (lb-in), kilogram-force-metres (kgf·m), or newton-centimetres (Ncm). Enter a value in any one and the rest update together, using the fixed ratios 1 lb-ft = 1.3558 Nm, 1 kgf·m = 9.80665 Nm (from standard gravity, since a kilogram-force is the weight of 1 kg), and 1 lb-in = 0.11298 Nm.
Different industries and eras standardized on different units for the same physical quantity: European bolt-torque tables and most modern torque wrenches read in Nm; American automotive manuals specify lb-ft for larger fasteners (wheel lugs, head bolts) and lb-in for smaller ones (interior trim, electronics); older Japanese and other Asian manuals often use kgf·m. A mechanic working from a mixed set of references — a European wrench and an American manual, say — has to convert, and that's exactly the situation this tool exists for.
Getting the conversion wrong has physical consequences, not just an inconvenient number. A classic error: a spec sheet lists "100 lb-ft" for a critical bolt, but the wrench is set in Nm and the number 100 gets dialed in unconverted. 100 lb-ft is actually 135.58 Nm — so a bolt torqued to "100 Nm" thinking it matched the spec is sitting at roughly 74% of the intended clamping force, about 26% loose. Under-torqued fasteners can work loose, vibrate, or fail to seal; over-torqued ones can strip threads, snap bolt heads, or crush gaskets — both failure modes trace back to a unit mix-up, not a bad wrench (see also this site's bolt-torque tool for the related tightening-sequence concept).
What to Know
- ft-lb vs lb-ft: for tightening torque, these are used interchangeably in practice — both mean pound-force times foot. Physics textbooks sometimes reserve ft-lb specifically for energy (dimensionally identical but conceptually different) — torque wrenches and repair manuals don't make that distinction.
- Small fasteners use smaller units: lb-in and Ncm exist because a value like "20 lb-ft" would be an awkward 0.02 on a lb-in-calibrated screwdriver — electronics enclosures, eyewear hinges, and precision screws are typically specified in lb-in or Ncm precisely to keep the numbers in a readable range.
- kgf·m depends on standard gravity: because kilogram-force is a weight, not a mass, its conversion to newton-metres (9.80665) bakes in Earth's standard gravitational acceleration — it's still a torque unit, just built from an older, gravity-based force definition rather than the newton.
- Always match the wrench to the spec's unit rather than converting in your head under time pressure — this tool exists specifically so you can check a number before it's on the bolt, not after.
Frequently Asked Questions
Is ft-lb the same as lb-ft?
For tightening torque, yes — both denote pound-force multiplied by foot, and every torque wrench, service manual and parts catalog treats them as identical. Physics courses sometimes reserve "ft-lb" specifically for units of energy or work, a dimensionally identical but conceptually distinct usage — that distinction doesn't carry over into mechanical torque specs.
Why does the converter include newton-centimetres?
1 Nm = 100 Ncm, and the unit shows up specifically where newton-metre values would be inconveniently small — precision screwdrivers, small servo motors, eyewear and electronics hardware. Keeping a fastener's spec in Ncm rather than a fraction of an Nm keeps the number easy to read and dial in accurately.
Why does getting the torque unit wrong actually break things?
Torque sets how tightly a fastener clamps two surfaces together. Under-torquing (from misreading a larger unit as a smaller one) leaves a joint loose enough to vibrate free, leak, or shift under load. Over-torquing (the reverse mistake) can stretch or snap the bolt, strip the threads, or crush a gasket or bearing race. Both are unit-conversion errors with a physical, sometimes safety-critical, consequence — not just an inconvenience.
Why does converting kgf·m to Nm involve the number 9.80665?
A kilogram-force is defined as the weight of one kilogram under standard Earth gravity, not a mass by itself — so turning a kgf-based torque value into the SI newton-metre requires multiplying by standard gravitational acceleration (9.80665 m/s²). It's a leftover of an older, gravity-based system of force units that some manuals — especially older Asian automotive documentation — still use.
How do I know which unit my torque wrench or spec sheet is actually using?
Check the wrench's scale markings directly — most dial or click-type wrenches print their unit (Nm, lb-ft, or occasionally both on a dual scale) right on the housing or scale. For a spec sheet, use the number's magnitude as a sanity check: automotive lug nuts are typically 80-150 in Nm but 60-110 in lb-ft, so a bare number without a stated unit is worth converting both ways and seeing which range makes sense for the fastener.
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Torque Unit Converter (Nm, lb-ft)
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