To convert HP to kW, simply multiply the value by 0.746: 1 HP = 0.746 kW. Conversely, to convert kW to HP, multiply by 1.341: 1 kW = 1.341 HP. For example, a 10 HP motor is 7.46 kW, while a 7.5 kW motor is approximately 10 HP.

On motor nameplates, gearbox catalogs and quotation forms, power may be expressed in HP, kW or sometimes simply as "horsepower." Torque and speed may also appear in different units and notations such as Nm, kgm, rpm and r/min. In this guide, you will find power conversions, the HP equivalents of standard motor ratings and other units commonly encountered when selecting a gearbox.

Formula for Converting HP to kW and kW to HP

Both units measure power; the only difference is the scale. There are two simple calculations that can be performed in seconds with a calculator:

• HP → kW: kW = HP × 0.746
• kW → HP: HP = kW × 1.341

The exact value is 1 HP = 745.7 watts. For everyday calculations, using 0.746 provides sufficient accuracy. A simple rule of thumb is also useful: approximately three-quarters of the HP value gives the equivalent kW value.

Conversion	Multiplier	Example
HP → kW	× 0.746	10 HP = 7.46 kW
kW → HP	× 1.341	7.5 kW = 10.06 HP
Metric horsepower (PS, BG) → kW	× 0.7355	10 PS = 7.36 kW
kW → Metric horsepower (PS, BG)	× 1.36	110 kW = 149.6 PS

Are HP, PS and Horsepower the Same?

Not exactly. There are two different units commonly referred to as "horsepower," and there is a difference of approximately 1.4% between them:

• HP (mechanical horsepower): 745.7 watts. It is of British-American origin and is generally the value used for electric motors and industrial applications.
• PS, CV or BG (metric horsepower): 735.5 watts. It is of European origin and is generally the "horsepower" value shown on vehicle and tractor registration documents.

Because the difference is small, both are commonly referred to simply as "horsepower" in everyday use. However, when performing calculations, it is important to know which horsepower unit is intended: 110 kW corresponds to 147.5 HP but 149.6 PS. For industrial electric motors, the easiest way to avoid this confusion is to perform calculations in kW.

Standard Motor Ratings: kW and HP Equivalents

Electric motors are not manufactured at every possible power rating; they are produced in specific standard increments. Motors commonly referred to on the market as "1 HP motor" or "3 HP motor" have the kW ratings shown below on their nameplates. Market names are rounded values, so they may not exactly match the calculated HP value.

Nameplate power (kW)	Calculated HP	Common market rating
0.37 kW	0.50 HP	0.5 HP
0.55 kW	0.74 HP	0.75 HP
0.75 kW	1.01 HP	1 HP
1.1 kW	1.48 HP	1.5 HP
1.5 kW	2.01 HP	2 HP
2.2 kW	2.95 HP	3 HP
3 kW	4.02 HP	4 HP
4 kW	5.36 HP	5.5 HP
5.5 kW	7.38 HP	7.5 HP
7.5 kW	10.06 HP	10 HP
11 kW	14.75 HP	15 HP
15 kW	20.12 HP	20 HP

The practical benefit of this table is as follows: if your old machine is marked "3 HP" and you need to order a replacement, the motor you should look for is not 2.24 kW but the standard rating of 2.2 kW. If the conversion result falls between two standard ratings, the next higher rating capable of handling the load is selected.

What Does the kW Value on a Motor Nameplate Indicate?

The power shown on the nameplate is the mechanical power delivered by the motor shaft; it is not the electrical power drawn from the mains. Due to efficiency losses, the electrical input power is always slightly higher. For example, a 5.5 kW motor with 90% efficiency draws approximately 6.1 kW from the mains at full load.

This distinction is important in two areas. For gearbox calculations, shaft power, meaning the nameplate value, is used. For electricity consumption, cable sizing or fuse calculations, the input power and current are taken into account. For more information about motor types and operating principles, see our article explaining the operating principle of asynchronous motors.

Why Is Power Alone Not Enough When Selecting a Gearbox?

A gearbox does not change the motor's power; it reduces speed and increases torque. Therefore, even if two machines use the same 2.2 kW motor, the required gearbox will differ if their output speeds are different. The key factor in selection is output torque, which is calculated from power and speed:

T (Nm) = 9550 × P (kW) ÷ n (rpm)

The formula uses kW. If your value is in HP, you must first convert it to kW; the most common mistake is entering the HP value directly into the formula, which overestimates torque by approximately one-third.

Example: Output Torque Calculation with a 3 HP Motor

Suppose a motor rated at 3 HP and 1400 rpm is connected to a gearbox with a reduction ratio of 28. For this example, let us assume a gearbox efficiency of 95%.

1. Convert the power to kW: 3 × 0.746 = 2.24 kW. The standard rating is 2.2 kW.
2. Calculate the motor torque: 9550 × 2.2 ÷ 1400 = 15 Nm.
3. Calculate the output speed: 1400 ÷ 28 = 50 rpm.
4. Calculate the output torque: 15 × 28 × 0.95 = approximately 399 Nm.

The rated torque of the selected gearbox must be sufficient to handle this value multiplied by the service factor. You can find step-by-step information on applying the service factor on our gearbox calculation page, and information on reduction ratio and speed in our gearbox speed calculation article.

Other Units Commonly Found in Gearbox Catalogs

Once the power unit is understood, gearbox catalogs typically include torque, speed and force columns. Since different manufacturers and older documents may use different notations, the most common units are summarized below.

Quantity	Units used	Conversion
Torque	Nm, daNm, kgm (kgf·m)	1 daNm = 10 Nm; 1 kgm = 9.81 Nm
Speed	rpm, r/min, min⁻¹	All three mean the same thing
Angular velocity	rad/s	rad/s = rpm × 0.1047
Shaft load (radial, axial)	N, daN, kgf	1 kgf = 9.81 N; 1 daN = 10 N
Reduction ratio (i)	Dimensionless	Input speed ÷ output speed

As a rough rule, treating 1 kgm as 10 Nm can provide a quick estimate in the field, but using 9.81 gives a more accurate result when making a selection. The logic behind torque units and other conversions such as lb·ft are explained in detail in our torque calculation article.

Common Mistakes When Converting Units

• Entering an HP value into the kW formula: The coefficient 9550 gives the correct result only when power is entered in kW.
• Treating HP and PS as identical: The difference is negligible for small motors, but at higher power levels it can result in a difference of several horsepower.
• Ordering the exact conversion result: There is no standard 2.24 kW motor; the nearest suitable standard rating must be selected.
• Assuming nameplate power is power consumption: The nameplate shows shaft power; the electrical power drawn from the mains is higher.
• Using output speed instead of motor speed: Motor torque is calculated using motor speed, while output torque is calculated using output speed.
• Confusing kgm with Nm: A value of 40 kgm in an old catalog is not 40 Nm but approximately 392 Nm.

If you are unsure about the power and torque values required for your application, you can review the points to consider when selecting a gearbox or contact us with information about the load, speed and operating duration.