Three-Phase Electric Motors by HP: kW Equivalents of 1–200 HP and Model Table

When choosing a replacement for a three-phase motor whose nameplate shows HP (horsepower), the right approach is to convert the HP value to kW and fit it to a standard kW rating: 1 HP equals about 0.746 kW, but motors are not built to the exact result of that calculation; they are built to IEC standard power ratings. In this article we bring together the kW equivalents of common values from 1/3 HP to 220 HP, HEM Motor's 1,500 rpm (4-pole) model for each rating, and the HP–kW mix-ups most often seen in the market.

The relationship between HP and kW: a short reminder

Two different horsepower definitions are found on electric motors. Mechanical (imperial) horsepower is 1 HP ≈ 0.746 kW, while metric horsepower (PS, CV) is ≈ 0.735 kW. The difference is negligible at small powers; what matters in motor selection is which standard rating the calculated value falls on. From HP to kW: kW = HP × 0.746; from kW to HP: HP = kW ÷ 0.746.

Calculating the power a machine needs from load, speed and torque is a separate topic; this article focuses on finding the correct model for a motor whose power is already known or read from an old nameplate.

HP – kW – model table (1,500 rpm, 4-pole)

The HP values in the table are the equivalents given for each model in HEM Motor product records; the kW column is the standard IEC power rating. The model column shows the 4-pole motor with 1,500 rpm synchronous speed; rated speed is the nameplate value. Between 0.55 and 11 kW there are also cast iron frame options with the same power and code; the table links the aluminium frame version.

All models are for 50 Hz; up to 3 kW the winding is 230/400 V, and from 4 kW upwards it is 400/690 V (Δ/Y). If you are looking for a 2-pole (3,000 rpm) or 6-pole (1,000 rpm) motor, the frame may be different at the same kW rating; you can see those options on the product pages or with the filters in the store. For current values see our electric motor current table, and for torque values our torque table.

Why don't the HP values in the table match the exact calculation?

The HP equivalents in the table are rounded commercial values. For example, 4 kW ÷ 0.746 ≈ 5.36 HP, but in the market this motor is called "5.5 HP"; 0.75 kW is exactly 1.005 HP and is referred to as "1 HP". The reason is that motors are built to kW ratings, not to HP, and HP is used only as an approximate label.

So after converting the HP value on an old nameplate, match the resulting figure to the nearest kW rating. 10 HP × 0.746 = 7.46 kW corresponds to the 7.5 kW rating; 25 HP × 0.746 = 18.65 kW corresponds to the 18.5 kW rating. Small differences are not a selection error.

"5.5 HP" or "5.5 kW"? The most common mix-up

The situation that causes the most confusion in the market is that the same figure exists both as an HP and as a kW rating. When someone says "a 5.5 motor", one person may mean 5.5 HP (i.e. 4 kW, 112M-4) and another 5.5 kW (i.e. 7.5 HP, 132S-4). The same applies to "7.5": 7.5 HP = 5.5 kW, while 7.5 kW = 10 HP (132M-4).

• Always write the unit when ordering: "5.5 kW" or "5.5 HP".
• As the table shows, these two powers are in different frames (112M and 132S); a wrong choice also affects mounting.
• On belt-and-pulley machines, look at the old motor's nameplate rather than relying on the technician's verbal description.
• HP is more common on small single-phase motors; apply the same conversion when switching to three-phase.

To see power and speed combinations side by side, review suitable HEM Motor models and current prices.

Choosing the correct kW from the HP on an old nameplate

If the nameplate of the motor to be replaced shows only HP, follow this order:

• Convert HP to kW: HP × 0.746. If the result is very close to a standard rating, take that rating.
• For a value in between, choose the next rating up: For example, 12 HP × 0.746 ≈ 8.95 kW; 7.5 kW is insufficient, so 11 kW is chosen. A rating one step lower would keep the motor permanently overloaded.
• Check the speed: If the nameplate speed is around 1,400–1,490, it is a 4-pole motor; around 2,800–2,980, 2-pole; around 900–990, 6-pole. Even with the same power, a different speed changes the machine's speed.
• Read the voltage and connection: 230/400 V or 400/690 V; your supply and starting method must match it.
• Compare frame and mounting: Is the IEC frame of the kW rating found from HP the same as the old motor's frame? Confirm the dimensions with the drawings on the technical drawings page.

If the nameplate is illegible, the motor's frame number is a good clue for estimating power; however, since power can change while the frame stays the same, the final choice should still be made using the nameplate or the machine manufacturer's information.

HP at higher powers: 100 HP and above

Although HP is used less for motors above 100 HP, it often appears in older plant documentation. The pairings 100 HP = 75 kW (280S-4), 125 HP = 90 kW, 150 HP = 110 kW, 180 HP = 132 kW and 220 HP = 160 kW appear in the table. A motor referred to as "200 HP" works out to about 149 kW; among the standard ratings, the next step up, 160 kW (220 HP), is considered as its equivalent. At these powers the motors have cast iron frames and 400/690 V windings; the starting method and supply line must be planned separately.

Hypothetical example: an old motor rated 15 HP

In a hypothetical workshop, suppose an old conveyor motor with "15 HP – 1450 rpm" on its nameplate is to be replaced. 15 × 0.746 ≈ 11.2 kW; this value is very close to the 11 kW rating, and commercially 11 kW is also listed as 15 HP. Since the speed is around 1,450, the 4-pole model is chosen: 160M-4. In the final step, the old motor's frame, mounting type and shaft end are compared with the drawing of the new model. If the old motor ran hot all the time and the load has increased, considering the next rating up, 15 kW, is also discussed at this stage.

Conclusion: convert HP to kW, fit it to a rating, verify the speed

When a power given in HP is multiplied by 0.746 and fitted to the nearest standard kW rating, the correct model is easy to find; for a value in between, the next rating up is preferred. Before ordering, prepare the power (with its unit), speed, mounting type, voltage, application and, if possible, a photo of the motor nameplate. All power and speed options are in our online store, and general family information is on the 3-phase electric motors page. Share a photo of your current motor's nameplate, its speed and mounting information via the nameplate submission page or contact us; request a quote for a suitable model.

Frequently Asked Questions

How many kW is 1 HP?

1 HP is about 0.746 kW. Commercially, a 1 HP motor corresponds to the 0.75 kW rating; in 4-pole form this model is the 80M2-4.

How many kW is a 5.5 HP motor?

5.5 HP is about 4 kW and corresponds to the 4 kW rating. A 5.5 kW motor, on the other hand, is about 7.5 HP; the two are in different frames.

What should I do if my calculated kW falls between two ratings?

Choose the next rating up. A motor one step lower runs continuously above its rated power and heats up; the higher rating leaves a reserve against the load.

Can I use the same motor if the HP value is the same but the speed is different?

No; even with the same power, a different speed changes the machine's speed and torque. Choose the number of poles that matches the old motor's speed.