Motor Power, Torque and Speed Calculator

Any two of shaft power, torque and speed give the third — in kW, HP, N·m, kgf·m, lb·ft, rpm or rad/s — plus the electrical power the motor has to draw to produce them.

Last updated 22 Sep 2026

Power, torque and speed

Any two of P, T, n → the third

What are you solving for?The quantity being solved for is locked and filled in.

Shaft powerThe motor’s nameplate rating is its shaft OUTPUT, not what it takes from the supply.

Power unit

Torque

Torque unit

SpeedUse the full-load speed from the nameplate, not the synchronous speed.

Speed unit

Motor efficiency (%)For the electrical input figure. 90.4% is the IEC 60034-30-1 IE3 value for a 7.5 kW 4-pole 50 Hz motor — an example. Read your own plate.

Electrical power in, mechanical power out of the shaft. The shaft power is the torque multiplied by the angular speed in radians per second; the difference between the two powers is the loss that heats the motor. No current is shown because this page is not told the supply voltage or the power factor — the motor full-load current page does that part.

49.22N·mExample

7.5 kW at 1,455 rpm, motor efficiency 90.4%

Power, torque and angular speed

P = T × ω ω = 2π × n ÷ 60 T = P ÷ ω = 9,549 × P_kW ÷ n P_electrical = P ÷ η

P: shaft (mechanical) power in watts — the nameplate rating of a motor
T: torque in newton metres
ω: angular speed in radians per second
n: speed in revolutions per minute
9,549: 60,000 ÷ 2π; ABB’s handbook rounds it to 9,550, which is 0.007% high
η: efficiency as a fraction — how much of the electrical input reaches the shaft

Worked example

7.5 kW at 1,455 rpm, motor efficiency 90.4%
ω = 2π × 1,455 ÷ 60 = 152.37 rad/s
T = P ÷ ω = 7,500 ÷ 152.37 = 49.22 N·m
Check with the handbook constant: 9,550 × 7.5 ÷ 1,455 = 49.23 N·m
That is 5.019 kgf·m or 36.31 lbf·ft
Electrical input = 7,500 ÷ 0.904 = 8.296 kW, so 796.5 W becomes heat
Running for an hour takes 8.296 kWh from the supply

Full-load torque at 50 Hz synchronous speeds (N·m)

Torque at the synchronous speed for each pole count. A real motor runs a few per cent slower than synchronous at full load, so its actual full-load torque is higher than these figures by the same few per cent — the 7.5 kW 4-pole example above is 47.7 N·m at 1,500 rpm and 49.22 N·m at its real 1,455 rpm.
Rating	2-pole, 3,000 rpm	4-pole, 1,500 rpm	6-pole, 1,000 rpm	8-pole, 750 rpm
0.37 kW	1.2	2.4	3.5	4.7
0.75 kW	2.4	4.8	7.2	9.5
1.50 kW	4.8	9.5	14.3	19.1
2.20 kW	7.0	14.0	21.0	28.0
3.70 kW	11.8	23.6	35.3	47.1
5.50 kW	17.5	35.0	52.5	70.0
7.50 kW	23.9	47.7	71.6	95.5
11.00 kW	35.0	70.0	105.0	140.1
15.00 kW	47.7	95.5	143.2	191.0
22.00 kW	70.0	140.1	210.1	280.1
37.00 kW	117.8	235.5	353.3	471.1
55.00 kW	175.1	350.1	525.2	700.3

Why torque, speed and power are one equation

Torque is a twist; speed is how fast the shaft turns; power is the rate at which the twist does work. Multiply the two and you have the third: P = T × ω. The only trap is that ω has to be in radians per second, not revolutions per minute, so a conversion of 2π/60 sits between the number on the nameplate and the number in the equation. Do it once and the rest is arithmetic — 7.5 kW at 1,455 rpm is 49.22 N·m, and the same 7.5 kW at half the speed would be twice the torque.

The nameplate rating is output, not input. A 7.5 kW motor delivers 7.5 kW at the shaft; it takes more than that from the supply. At the IE3 efficiency for that size, 90.4%, the input is 8.296 kW and 796.5 W is lost as heat inside the machine. This catches people sizing a generator, a cable or an inverter from the nameplate kW: use the input power, and then the current, which the motor full-load current calculator works out.

Horsepower is three different numbers. Mechanical horsepower — 550 foot-pounds-force per second — is 745.6999 W. Metric horsepower, the PS or CV that European and Indian catalogues mean, is 75 kilogram-force metres per second, which is 735.49875 W. Electrical horsepower is defined as exactly 746 W. The spread between the largest and the smallest is 1.4%. That sounds like rounding until you notice that 7.5 kW is 10.06 mechanical horsepower but 10.20 metric — the second one reads as a 10 HP motor and the first does not quite. The HP to kW converter sets all three side by side.

Torque units. N·m is the SI unit and the one every calculation should use. kgf·m, still printed on Indian and Japanese plates, is 9.80665 N·m. lbf·ft, on American plates, is 1.3558 N·m. A “foot-pound” of torque and a “foot-pound” of energy are the same size and different quantities, which is why the torque one is properly written lbf·ft.

What this page does not know. It has no idea whether your motor can actually produce that torque at that speed. An induction motor’s torque rises from its locked-rotor value to a breakdown peak and then collapses; the full-load point is a small part of that curve. Use the induction motor slip calculator for where the machine really sits, and the BLDC inverter loss calculator if the shaft is driven by an inverter rather than straight off the mains.

Frequently asked questions

How do I calculate motor torque from kW and rpm?

Torque in newton metres = power in watts ÷ (2π × rpm ÷ 60). For 7.5 kW at 1,455 rpm that is 7,500 ÷ 152.37 = 49.22 N·m. The shortcut form is T = 9,549 × kW ÷ rpm.

What is the 9550 in the motor torque formula?

It is 60,000 ÷ 2π, the constant that lets you put kilowatts and rpm straight into a torque formula. The exact value is 9,549; handbooks round it to 9,550, which is 0.007% high — far inside any nameplate tolerance.

Is a motor’s kW rating what it draws from the supply?

No. It is the mechanical power at the shaft. The electrical input is that divided by the efficiency — 8.296 kW for a 7.5 kW motor at 90.4%. Size supplies, cables and generators from the input, never from the nameplate kW.

How do I convert N·m to lb-ft or kgf·m?

Divide by 1.3558 for lbf·ft and by 9.80665 for kgf·m. One newton metre is 0.7376 lbf·ft or 0.1020 kgf·m.

Does torque change if I use a gearbox?

Yes, and in the opposite direction to speed. A 10:1 reduction gives ten times the torque at one tenth the speed, less the gearbox’s own losses — power is what is conserved, not torque.

Related calculators

References

ABB. Softstarter Handbook, publication 1SFC132060M0201. Direct-on-line starting current “Usually between 6-8 times the rated current, but it can be more than 10 times the rated current”; star-delta: “The resulting current when Y-connected will be 1/3 of the current when delta connected” and the torque “ending up being 33% of the torque available when delta connected”; n = 2 × f × 60 / p; s = (n₁ − n)/n₁; T_n = 9550 × P_r/n_r.
National Institute of Standards and Technology. Guide for the Use of the International System of Units (SI), Special Publication 811, Appendix B.8, factors for units listed alphabetically: horsepower (550 ft·lbf/s) = 7.456 999 × 10² W, horsepower (metric) = 7.354 988 × 10² W, horsepower (electric) = 7.46 × 10² W, horsepower (boiler) = 9.809 50 × 10³ W.
IEC 60034-30-1 efficiency classes for line-operated AC motors (IE1 standard, IE2 high, IE3 premium, IE4 super-premium), as tabulated in ABB technical note 9AKK107319 EN 05-2018. At 50 Hz and 4 poles the nominal efficiencies are 79.6 / 82.5 / 85.7% at 0.75 kW, 85.5 / 87.7 / 90.4% at 3 kW, 88.7 / 90.4 / 92.6% at 7.5 kW and 91.6 / 93.0 / 94.5% at 22 kW for IE2 / IE3 / IE4.
Chapman S J. Electric Machinery Fundamentals, 5th ed. McGraw-Hill, 2012. Chapter 2, Transformers — the ideal transformer, the turns ratio, impedance transformation and voltage regulation; chapter 6, Induction Motors — synchronous speed, slip, rotor frequency and induced torque.