Tool 15 · Reference
One servo is rated 12 kg·cm, one stepper 0.45 N·m, one gearmotor 85 oz·in. Same quantity, three dialects. Convert between all of them here — and see what the number actually means in terms of lifting something real.
How far from the shaft the load hangs
Enter a torque value and a lever arm greater than zero.
Equivalent values
torque = force × distance
1 kg·cm = 0.0980665 N·m · 1 N·m ≈ 10.197 kg·cm
1 oz·in = 0.00706155 N·m · 1 lb·in = 0.112985 N·m
load (kg) = torque (N·m) ÷ (9.81 × arm in metres)
Every torque unit is a force unit multiplied by a distance unit, which is why there are so many of them — pick a force (kilogram-force, newton, ounce, pound) and a distance (cm, m, inch, foot) and you have another perfectly valid name for the same physical quantity. The only trap is that kg·cm and g·cm use kilogram-force, a unit of weight rather than mass, which is where the 9.81 keeps appearing.
The lever-arm figure on the nameplate is what makes torque intuitive. Torque alone doesn't tell you what a motor can lift; torque divided by distance does. A 20 kg·cm servo sounds mighty until you hang the load 20 cm out on an arm, where it manages 1 kg — before any safety factor. That relationship is the whole basis of sizing a robot arm, worked through joint by joint in the Servo Torque Calculator.
On the safety factor: hobby servo and DC motor ratings are almost always stall figures — the torque at the instant the motor stops turning, which it cannot sustain without overheating or stripping gears. Designing at a third of the rated number is normal practice for servos, and it's why the default here is 3×. Stepper holding torque is a different kind of number again, and it falls off sharply with speed, as the Stepper Motor Calculator shows.
Rough anchors to sanity-check a spec: a micro SG90 servo is about 1.8 kg·cm (0.18 N·m); a standard MG996R around 10 kg·cm (0.98 N·m); a typical NEMA 17 stepper holds 40 N·cm (0.4 N·m, ≈4 kg·cm); a 37 mm gearmotor at a 100:1 ratio might deliver 2 N·m (20 kg·cm). If a cheap listing claims ten times these figures for the same physical size, the number is aspirational.
Yes — kgf makes the "kilogram-force" explicit, which is technically the correct notation. Hobby listings almost always drop the f, and mean the same thing.
Power needs speed as well: watts = torque (N·m) × speed (rad/s), or watts ≈ torque (N·m) × RPM ÷ 9.55. A motor's torque figure alone says nothing about how fast it can do the work — the Motor Sizing Calculator handles both together.
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