Kilowatts to Horsepower Calculator
A European pump manufacturer's spec sheet rates the motor at 15 kW. The US distributor's catalog lists the same physical motor at 20 HP. Same shaft, same impeller, same bearing frame, two power ratings from two different measurement systems, and neither number is wrong. Kilowatts measure real power directly; horsepower is an older imperial unit built around an 18th-century estimate of how much work a draft horse could sustain. Converting between them is arithmetic, not guesswork, once the constant that links the two units is known, and it's the same arithmetic whether the motor is a fractional-horsepower fan or a 37 kW industrial pump.
HP = 15 / 0.7457 = 20.12 HP
Why the two ratings coexist
Most of the world's electrical equipment is rated under IEC standards, which specify motor output in kilowatts, a direct SI unit of power. NEMA, the standard used across North America, has historically rated the same class of motor in horsepower, a unit inherited from the days when a machine's output was sized by comparison to the animals it replaced. Neither convention is being phased out; a pump, compressor or fan bought from a European or Asian manufacturer is still very likely to arrive with a kW-only nameplate, and it has to be translated before it fits into a US-style spec sheet, motor schedule or parts catalog.
The two figures aren't measuring different things: output shaft power is output shaft power, regardless of which unit records it. What differs is only the yardstick, and the conversion factor between them is fixed and unchanging, unlike a voltage or a power factor that varies by installation.
That distinction matters most at the moment of a parts search or a replacement order, when a distributor's kW-labeled catalog entry has to be checked against a maintenance record, a purchase order or a NEMA-style spec sheet written in horsepower. Getting the number itself right is the easy part; the harder part, covered further down this page, is remembering that a matching power figure is a necessary check, not a sufficient one, for a true motor replacement.
Where the 0.7457 constant comes from
One mechanical horsepower (also called imperial horsepower, the figure used throughout US motor catalogs and NEMA documentation) is defined as 745.7 watts, tracing back to James Watt's 18th-century estimate of a horse's sustained work rate. Converting kilowatts to horsepower means dividing by that constant expressed in kilowatts, 0.7457:
Going the other direction multiplies by the same constant: kW = HP × 0.7457. There's a second, less common horsepower, the metric horsepower (PS), defined slightly differently at 735.5 watts, but the mechanical/imperial figure above is what this calculator and every table on this page use, matching NEMA convention.
Because the constant is a straight ratio rather than a rounded approximation, the conversion is exact in both directions and doesn't accumulate error however many times it's applied. Converting a whole motor schedule from kW to HP and back again returns the original kW figures to within normal rounding.
Worked example: converting a 15 kW motor nameplate
IEC-rated pump motor, 15 kW output, converting to the HP figure a US spec sheet expects.
- 1
Divide by the horsepower constant
HP = 15 / 0.7457
- 2
Solve
15 / 0.7457 = 20.1153 HP
- 3
Round to a practical spec-sheet figure
20.1153 HP → 20.12 HP
This converts output power only. Voltage, frequency, frame size, mounting and duty cycle still have to be checked separately before a converted HP figure is treated as a confirmed replacement match. Confirm against the equipment manufacturer's documentation.
Standard IEC motor sizes, kW to HP
IEC motors are built in standardized kW steps, not round-number horsepower steps, which is why the converted HP figures below land on numbers like 20.12 or 29.50 rather than clean round values. The 15 kW row is highlighted to match the worked example above; the rest of the table covers the common IEC frame sizes on either side of it, from a small 0.75 kW fan or pump motor up to a 37 kW industrial unit.
| Rated power (kW) | Horsepower (HP) |
|---|---|
| 0.75 kW | 1.01 HP |
| 1.5 kW | 2.01 HP |
| 3 kW | 4.02 HP |
| 5.5 kW | 7.38 HP |
| 7.5 kW | 10.06 HP |
| 11 kW | 14.75 HP |
| 15 kW | 20.12 HP |
| 22 kW | 29.50 HP |
| 37 kW | 49.62 HP |
Reference figures only, rounded to two decimal places: the kW value is mechanical output power, not electrical input power, and any real nameplate should be confirmed against its own documentation.
More motor-rating conversions
Questions
Kilowatts to horsepower FAQ
Motor-nameplate questions that come up once an IEC kW rating has to be matched against a NEMA HP spec.
Why are IEC motors rated in kilowatts while NEMA motors are rated in horsepower?
IEC and NEMA are two independent standards bodies that never converged on a single unit for motor output power, so the region a motor was built for still determines whether the nameplate reads in kW or HP. IEC-standard motors, common across Europe, Asia and most of the rest of the world, use kilowatts because it's the direct SI unit of power. NEMA, the North American standard, kept horsepower for historical continuity with the imperial unit system used across US industry. A motor can be manufactured to either standard regardless of where it's installed, which is why a kW-only nameplate still turns up on equipment sold in the US.
Is a "15 kW" motor exactly 20 HP?
No. 15 kW converts to 20.1153 HP, not an even 20 HP, and vendor literature that rounds it to "20 HP" is naming the nearest standard NEMA frame size, not stating a literal unit equivalence. The precise conversion, 15 / 0.7457 = 20.1153 HP, doesn't land on a round number because kilowatts and horsepower are built around different physical increments. Catalogs and cross-reference tables often round to the nearest common HP rating for ordering convenience, which is a labeling shortcut, not a change in the underlying arithmetic.
Why do standard motor sizes look round in one system but not the other?
Because IEC and NEMA each standardized their own step sizes independently, and a unit conversion doesn't preserve round numbers across two unrelated numbering systems. IEC frame sizes follow round kilowatt steps: 0.75, 1.5, 3, 5.5, 7.5, 11, 15, 22, 37 kW and so on, spaced evenly in metric units. NEMA sizes follow round horsepower steps: 1, 2, 3, 5, 7.5, 10, 15, 20, 25, 30, 40 HP, spaced evenly in imperial units. Converting one system’s round numbers into the other unit almost never produces a round number back, which is exactly what the reference table above shows.
What else should I check before treating a kW-to-HP conversion as a full motor replacement match?
The output power rating is only one line on a motor nameplate: a straight kW-to-HP conversion says nothing about voltage, frequency, frame size, mounting, poles or duty cycle, all of which also have to match for a real replacement. A European 15 kW motor built for 400 V, 50 Hz service is not a drop-in swap for a US motor built for 460 V, 60 Hz, even though the power figures line up almost exactly. As general reference, treat the converted HP number as the starting filter in a parts search, then confirm the rest of the nameplate, ideally with the equipment manufacturer or a qualified electrician, before ordering a replacement.
Is the kW figure on a motor nameplate the mechanical output or the electrical input?
It's mechanical output, the shaft power the motor delivers to whatever it's driving, not the electrical power the motor draws from the supply. Electrical input power is higher than the kW nameplate figure because no motor converts electricity to shaft work at 100% efficiency; the gap between the two is the motor's rated efficiency. A 15 kW-output motor running at roughly 91% efficiency draws close to 16.5 kW electrically, so the nameplate kW figure alone understates the load a circuit actually has to supply.
Does the 0.7457 constant change for different motor types, like a "metric horsepower"?
No. For mechanical/imperial horsepower, 0.7457 kW is fixed regardless of motor type, though a separate "metric horsepower" (PS) unit sometimes seen on older European equipment uses a slightly different constant. Metric horsepower (PS or CV) is defined as 735.5 watts rather than 745.7 watts, a difference of about 1.3%. US and NEMA motor documentation uses the mechanical/imperial horsepower and the 0.7457 constant throughout, which is also what this calculator and page use, so a PS figure from older European literature needs its own separate conversion before being compared.