Torque Converter
One value in, all four torque units out — before you set the wrench.
Typical torque specs
Typical ranges only — always use the figure printed in your vehicle or component manual.
Nm to lb-ft, and the three other units you will meet
Torque is force applied at a distance from a pivot, so every unit is a force unit multiplied by a length unit. The SI version is the newton metre (Nm). The workshop standard in the United States is the pound-foot (lb-ft), and for small fasteners the pound-inch (lb-in), which is exactly one twelfth of a lb-ft. Older Japanese and European manuals use the kilogram-metre (kg-m or kgf-m), the force of one kilogram under gravity acting on a one-metre arm.
The only four numbers that matter: 1 lb-ft = 1.355818 Nm, 1 lb-in = 0.1129848 Nm, 1 kg-m = 9.80665 Nm. Everything this converter does is multiply into newton metres and divide back out, which keeps every unit rounded from the same underlying value rather than from each other.
Worked example: a wheel that has to stay on
A workshop manual specifies 110 Nm for the lug nuts. Your click wrench is marked in lb-ft. Divide: 110 ÷ 1.355818 = 81.1, so set the wrench to 81 lb-ft — most wrenches adjust in 1 lb-ft steps, so 81 is exactly reachable. Going the other way, an American truck spec of 150 lb-ft is 150 × 1.355818 = 203 Nm, which is why metric wrenches for pickup work need a range that reaches past 200 Nm.
Small fasteners flip the problem. A carbon bicycle stem is typically 5 Nm. In lb-ft that is 3.7 — an unusable setting on a wrench whose bottom scale mark is 10 lb-ft. Convert to pound-inches instead: 5 ÷ 0.1129848 = 44.3 lb-in, which sits mid-scale on a small 20-80 lb-in wrench. Choosing the right unit is really choosing the right tool.
What over-tightening actually does
A bolt is a spring. Tightening stretches it, and the stretch is what clamps the joint. Torque is an indirect way of measuring that stretch, which is why the number matters more than it looks. Push past the bolt's yield point and it stays stretched: the clamping force drops, the thread pitch distorts, and the fastener will not hold the next time it is tightened. Wheel studs snapped on the driveway almost always started as a guessed setting or an impact gun on maximum.
Under-tightening is quieter and just as dangerous. A wheel that is 30 percent light on clamp load lets the mating surfaces move a fraction of a millimetre with every corner, the nuts back off, and the stud holes start to elongate. On aluminium and magnesium parts — engine covers, spark plug threads, brake calipers with alloy carriers — the damage runs the other way: the threads in the soft part strip long before the steel bolt complains. A 20-30 Nm spark plug in an aluminium head is 15-22 lb-ft, and there is no honest way to feel the difference between 22 and 40 by hand.
Torque wrench technique in ninety seconds
Clean and lightly lubricate the threads unless the manual says dry, because a rusty thread can absorb a third of your applied torque in friction and leave the joint loose at the correct reading. Pull smoothly on the handle at the marked grip point; a jerk overshoots the click. Stop at the first click rather than chasing a second one. Tighten multi-bolt patterns in a star sequence, and on wheels re-check after 50-100 km. Store click wrenches wound back to their lowest setting, and have them calibrated every year or so if they are used regularly — a good click wrench is accurate to roughly ±4 percent, and that tolerance drifts.
Why two systems exist at all
The pound-foot descends from imperial engineering practice and survives because American tool inventories, fastener charts and technician habits are built around it. The newton metre arrived with SI in 1960 and is now the unit of every engineering standard and nearly every non-US manual. The kilogram-metre is the awkward middle child: metric in length and mass, but based on gravity rather than the newton, which is why it was retired from standards work yet still appears on classic Japanese motorcycle manuals and older beam wrenches. If a manual says 10.5 kg-m, that is 103 Nm, or 76 lb-ft.
Limits of a conversion
This tool converts units; it does not tell you the correct specification. Torque figures depend on bolt grade, thread size, whether the thread is dry, oiled or has thread-locker on it, and whether the manufacturer specifies a torque-plus-angle procedure — many modern head and suspension bolts are torque-to-yield and must be replaced, not re-tightened. Always take the number from the manual for your exact model and year, convert it here, and set the wrench to the converted figure rather than to something that felt about right.
Sources & further reading
Frequently asked questions
Which is bigger, a newton metre or a pound-foot?
A pound-foot is bigger. One lb-ft equals 1.355818 Nm, so 100 Nm is about 73.8 lb-ft. Because the number shrinks going from Nm to lb-ft, a spec that looks low in lb-ft can still be exactly the same tightness.
My torque wrench reads lb-ft but the manual says Nm. What now?
Convert it, never estimate it. Divide the Nm figure by 1.356 to get lb-ft: 110 Nm becomes 81 lb-ft. Guessing in this range is how wheel studs get stretched or snapped, and an under-torqued wheel can work loose on the road.
Why do older Japanese manuals use kg-m?
kg-m (kgf-m) is the metric gravitational unit that was standard before SI took over, and 1 kg-m equals 9.80665 Nm. Older Japanese and European service manuals, plus many beam wrenches, are still marked this way. A 10.5 kg-m spec is 103 Nm, or 76 lb-ft.
How does torque relate to horsepower?
Torque is twisting force; power is that torque multiplied by rotational speed (P = T × ω). An engine making 400 Nm at 3,000 rpm puts out roughly 126 kW, about 169 hp. Converting torque units never changes the power — it is the same twist written differently.