Free tool
Motor torque converter
Type a torque into any box and the other seven follow: N·m, N·cm, mN·m, kg·cm, gf·cm, oz·in, lb·in and lb·ft, worked out from the exact definitions of the newton, the kilogram-force and the pound-force.
- N·m
- 1.2
- N·cm
- 120
- mN·m
- 1200
- kg·cm (kgf·cm)
- 12.237
- gf·cm
- 12237
- oz·in (ozf·in)
- 169.93
- lb·in (lbf·in)
- 10.621
- lb·ft (lbf·ft)
- 0.88507
kg·cm on a datasheet means kgf·cmA kilogram is a mass, not a force. 1 kg·cm is the weight of 1 kg at standard gravity acting on a 1 cm arm: 0.0980665 N·m. Multiplying N·m by 10 therefore comes out about 2% short of the true kg·cm figure.
Holding torque is not running torqueA datasheet's headline torque is measured standing still. What a stepper delivers while moving falls as speed rises: see holding torque and running torque.
Holding torque of the stepper motors in our catalogue
Every stepper motor on this site whose specifications list a holding torque, grouped by NEMA frame size. The N·m column is the figure on the product page. The other columns are converted from it to four significant figures, so they can differ in the last digit from a rounded kg·cm figure printed on the product page. Flange is the size the product lists.
How it is worked out
Every box is converted through the newton metre. The value you type is multiplied by how many N·m one of its unit is, and that N·m figure is divided by the same number for each of the other units. The box you type in keeps exactly what you typed; the others are rounded to the number of significant figures you choose.
torque in N·m = value × (N·m per unit typed in) torque in unit X = torque in N·m ÷ (N·m per unit X)
Holding torque and running torque
Holding torque is the torque it takes to force round the shaft of a stepper motor that is powered, standing still, with rated current in its windings. It is the one number every stepper datasheet leads with, and the one in most product names, including the table above.
Running torque is what the motor can deliver while it is stepping. Datasheets give it as a pull-out torque curve against speed, and it falls as speed rises: each winding's inductance limits how quickly the drive can build up current before the next step arrives, so at speed the current, and the torque with it, never reaches its full value. A higher supply voltage, within what the drive and motor are rated for, holds the torque up to a higher speed.
- Size a motor from the torque it must deliver at its working speed, read off the pull-out curve, with margin for friction, cutting load and the torque needed to accelerate the load. Holding torque alone overstates what a moving axis gets.
- The holding torque figure assumes rated current. A drive set below the motor's rated current gives less torque than the datasheet figure.
- Microstepping makes motion smoother; it does not add torque.
- Detent torque, the slight notchiness felt when turning an unpowered stepper, is a much smaller figure and a different thing.
All of these are torques, so any of them converts here in the same way.
Why kg·cm is really kgf·cm
Torque is a force times the length of the arm it acts on. A kilogram is a mass, so "kilogram centimetre" is not a torque at all. What a datasheet means by kg·cm is the kilogram-force centimetre: the weight of a 1 kg mass under standard gravity, hanging from an arm 1 cm long.
The kilogram-force is defined with standard gravity, g0 = 9.80665 m/s², not with the gravity where you happen to stand, so it is an exact and fixed amount of force: 1 kgf = 9.80665 N. That makes 1 kgf·cm = 9.80665 N × 0.01 m = 0.0980665 N·m. The common shortcut of treating 1 N·m as 10 kg·cm is about 2% off, because the true figure is 10.19716.
The same is true of every unit here with a mass in its name. g·cm is gram-force centimetres; oz·in and lb·in are ounce-force and pound-force inches. The pound-force is the weight of the international pound, defined as exactly 0.45359237 kg, under the same standard gravity.
The conversion factors
Every factor comes from these exact definitions, and nothing else.
1 in = 0.0254 m exact, by definition 1 ft = 0.3048 m exact, by definition g0 = 9.80665 m/s² standard gravity, exact 1 kgf = 1 kg × g0 = 9.80665 N 1 lbf = 0.45359237 kg × g0 = 4.4482216152605 N 1 ozf = 1 lbf ÷ 16 = 0.27801385095378125 N
| Written as | Strictly | Built from | 1 of the unit, in N·m (exact) | 1 N·m, in the unit |
|---|---|---|---|---|
| N·m | newton metre | the SI unit | 1 | 1 |
| N·cm | newton centimetre | 1 N × 0.01 m | 0.01 | 100 |
| mN·m | millinewton metre | 0.001 N × 1 m | 0.001 | 1000 |
| kg·cm | kilogram-force centimetre, kgf·cm | 9.80665 N × 0.01 m | 0.0980665 | 10.19716 |
| gf·cm, g·cm | gram-force centimetre | 0.00980665 N × 0.01 m | 0.0000980665 | 10197.16 |
| oz·in | ounce-force inch, ozf·in | 0.27801385095378125 N × 0.0254 m | 0.00706155181422604375 | 141.6119 |
| lb·in | pound-force inch, lbf·in | 4.4482216152605 N × 0.0254 m | 0.1129848290276167 | 8.850746 |
| lb·ft | pound-force foot, lbf·ft | 4.4482216152605 N × 0.3048 m | 1.3558179483314004 | 0.7375621 |
The fourth column is exact. The last is its reciprocal, which never ends, rounded to seven significant figures. Two useful relations fall straight out: 1 lb·in = 16 oz·in, and 1 lb·ft = 12 lb·in.
Worked example
A motor datasheet from an American supplier gives a holding torque of 280 oz·in, and you want to compare it with motors listed in N·m and kg·cm.
to N·m: 280 oz·in × 0.00706155181422604375 N·m per oz·in = 1.9772 N·m to kg·cm: 1.9772 N·m ÷ 0.0980665 N·m per kg·cm = 20.162 kg·cm check: 280 oz·in ÷ 16 oz·in per lb·in = 17.5 lb·in
So 280 oz·in is 1.9772 N·m, or 20.162 kg·cm. The multiply-by-10 shortcut would have given 19.77 kg·cm, about 2% low. Type 280 into the oz·in box above to see all eight units at once.
Related Tiny Controls products
The current set on a stepper drive decides how much of a motor's rated torque you actually get. Tiny Controls makes the Tstep stepper drives, among them the Tstep-087X (18–80 V DC, 1.2–7.0 A), the Tstep-117X (18–110 V DC or 18–80 V AC, 1.2–7.0 A) and the Tstep-168X (24–160 V DC or 18–110 V AC, 1.2–8.0 A). Motors, drives and controllers are all on the products page.