Convert between mechanical horsepower, kilowatts, metric horsepower (PS) and watts, work out the torque a motor delivers from its power and speed, or the power from a torque and speed. Includes tables of common motor ratings in both horsepower and kilowatts.
Worked example
These are example values. Change any entry above and press Calculate to run your own numbers.
Kilowatts (kW)
7.457
Horsepower (mechanical hp)
101 hp = 745.7 W
Metric horsepower (PS)
10.139 1 PS = 735.5 W
Watts (W)
7,457
BTU per hour
25,444 heat equivalent of the same power
A motor nameplate in hp or kW is the shaft output power. The electrical input is higher by the motor efficiency; use the kW to amps calculator for current.
How it works
North American motors are rated in horsepower and most of the rest of the world rates them in kilowatts. The two are linked by a fixed factor, and torque follows from power and speed, which is why a slower motor of the same power produces more torque.
The formulas
1 hp (mechanical) = 745.7 W = 0.7457 kW; 1 kW = 1.3410 hp
1 PS (metric horsepower) = 735.5 W = 0.7355 kW
Torque (N·m) = 9,549 × power (kW) ÷ speed (rpm)
Torque (lbf·ft) = 5,252 × power (hp) ÷ speed (rpm)
Power = torque × angular speed = T × 2π × rpm ÷ 60
Reference tables
Common motor ratings in horsepower, with the kW equivalent
hp
kW
0.5
0.3728
0.75
0.5593
1
0.7457
1.5
1.119
2
1.491
3
2.237
5
3.728
7.5
5.593
10
7.457
15
11.19
20
14.91
25
18.64
30
22.37
40
29.83
50
37.28
60
44.74
75
55.93
100
74.57
125
93.21
150
111.9
200
149.1
250
186.4
300
223.7
Standard IEC motor ratings in kW, with the horsepower equivalent
kW
hp
0.18
0.2414
0.25
0.3353
0.37
0.4962
0.55
0.7376
0.75
1.006
1.1
1.475
1.5
2.012
2.2
2.95
3
4.023
4
5.364
5.5
7.376
7.5
10.06
11
14.75
15
20.12
18.5
24.81
22
29.5
30
40.23
37
49.62
45
60.35
55
73.76
75
100.6
90
120.7
110
147.5
132
177
160
214.6
200
268.2
Frequently asked questions
How do you convert hp to kW?
Multiply horsepower by 0.7457. Ten horsepower is 7.457 kW. To go the other way, multiply kilowatts by 1.341: 7.5 kW is 10.06 hp. The calculator applies the exact mechanical horsepower of 745.7 W.
What is the difference between hp and PS (metric horsepower)?
Mechanical horsepower is 745.7 W and metric horsepower (PS, CV or pferdestärke) is 735.5 W, so the two differ by about 1.4%. Motors in North America use mechanical horsepower; some European equipment quotes PS. Where it matters, convert both to kW.
How do I work out motor torque from hp and rpm?
Use torque (lbf·ft) = 5,252 × hp ÷ rpm, or torque (N·m) = 9,549 × kW ÷ rpm. One horsepower at 1,800 rpm gives about 2.92 lbf·ft, or 3.96 N·m. Because rpm is in the denominator, a 4-pole motor (about 1,800 rpm) gives roughly twice the torque of a 2-pole motor (about 3,600 rpm) at the same power.
Is the nameplate hp the electrical input power?
No. The hp or kW on a motor nameplate is the mechanical power at the shaft. The electrical power drawn is higher by the motor's losses, which the efficiency describes. For the current a motor draws, use the kW to amps calculator with the efficiency and power factor.
What are the standard kW ratings for IEC motors?
IEC motors are built in a standard series of kW ratings, such as 0.75, 1.1, 1.5, 2.2, 3, 4, 5.5, 7.5, 11, 15, 18.5, 22, 30, 37, 45, 55, 75, 90 and 110 kW. The table on this page lists them with their horsepower equivalents, so you can see which IEC rating is closest to a given hp.
