HP to kW & kW to HP Calculator

To convert HP to kW, multiply horsepower by 0.746 — for example, 10 HP = 10 × 0.746 = 7.46 kW. To convert kW to HP, divide kilowatts by 0.746 — for example, 7.46 kW ÷ 0.746 = 10 HP. Horsepower (HP) and kilowatts (kW) are two different units used to express the same physical quantity: power, the rate at which work is done. Horsepower dates back to the 18th century, when engineer James Watt needed a way to compare the output of his early steam engines to the pulling capacity of a horse, since horses were the dominant source of mechanical power at the time. The unit stuck, and even today it remains the standard way many motor, engine, and pump nameplates express their rated power, particularly in the United States and on older or imported industrial equipment.

The kilowatt, by contrast, is part of the International System of Units (SI) and is the standard unit of power used almost everywhere else in electrical and mechanical engineering — on motor nameplates, generator ratings, and transformer specifications. (Note that electricity bills are based on energy — kilowatt-hours, kWh — not power in kW; kW measures the rate of doing work at an instant, while kWh measures energy consumed over time.) Because HP and kW measure the exact same physical quantity, just scaled differently, the conversion between them is a fixed, unchanging constant: 1 mechanical HP equals approximately 0.7457 kW, commonly rounded to 0.746 kW in engineering practice — the figure this calculator uses by default. This means converting in either direction is a simple multiplication or division — no other variables like voltage, current, or power factor are involved, unlike a conversion to kVA.

Precision note: This calculator uses 0.746 kW per mechanical HP — a rounded form of the more precise 0.7457 kW conversion — matching the figure printed on most motor and pump nameplates. Wherever this page mentions 0.7457, it refers to the unrounded value the 0.746 figure is derived from; both describe the same mechanical HP definition.

How to Convert HP to kW (Step by Step)

1. Confirm which horsepower definition your nameplate or datasheet uses — mechanical (imperial), metric (PS/CV), or boiler HP — since each uses a different conversion factor.
2. For mechanical HP, multiply the horsepower value by 0.7457 (commonly rounded to 0.746) to get kilowatts.
3. For metric HP (PS/CV), multiply by 0.7355 kW instead.
4. For boiler HP, multiply by approximately 9.8095 kW — do not use the mechanical HP factor.
5. To go the other way, divide the kilowatt value by the same factor to recover horsepower.

This conversion is used constantly in real engineering work: comparing an imported pump rated in HP against a locally available motor rated in kW, cross-checking nameplate data between two pieces of equipment specified in different unit systems, or converting an engine's HP rating into kW for inclusion in an SI-based technical report or specification sheet.

Worked example: Suppose an imported water pump is nameplated at 15 HP, and you need its rating in kW to match against a locally available motor. Using the formula: kW = 15 × 0.746 = 11.19 kW. This 11.19 kW figure is the pure unit conversion — it does not by itself tell you which standard motor to buy. The appropriate available motor rating must be selected after checking the driven load's torque and duty requirements, running speed, starting requirements, service factor, voltage, frequency, and the manufacturer's own rating data — not from the converted number alone. Conversely, if a generator is rated at 25 kW and you need its equivalent in horsepower for an older specification sheet: HP = 25 ÷ 0.746 ≈ 33.51 HP — useful when comparing against engine-driven generator sets that are typically rated in HP rather than kW.

Shaft Power vs Electrical Input Power

It's worth being clear about what an HP or kW nameplate rating generally describes: for motors, the rated HP or kW generally represents mechanical shaft output power — the useful rotational power delivered at the shaft — not the electrical power drawn from the supply. Because no motor is 100% efficient, the electrical input power is always somewhat higher than the shaft rating, with the difference lost as heat, friction, and magnetic losses. To estimate electrical input power: input kW = shaft kW ÷ efficiency (typically 0.85–0.95 for standard industrial motors). To go further and estimate input current, the formula differs by supply type and must also account for efficiency, not just voltage and power factor:

• Single-phase: I = (Shaft kW × 1000) ÷ (Efficiency × V × PF)
• Three-phase: I = (Shaft kW × 1000) ÷ (√3 × Efficiency × V × PF)

Here V is supply voltage, PF is power factor, and Efficiency is the motor's rated efficiency as a decimal. Skipping the efficiency term or the √3 factor (for three-phase) is a common source of undersized cable and breaker calculations — see the kW to Current calculator for a worked version of this calculation.

Common Mistakes When Converting HP to kW

• Treating the nameplate HP/kW figure as electrical input power. It is shaft output power; the actual power drawn from the mains is higher due to motor losses (efficiency) and, for AC motors, is further related through power factor if converting to current.
• Mixing up metric and mechanical horsepower. Mechanical (imperial) horsepower uses 0.746 kW, while metric horsepower (PS, common on older European and Japanese equipment) is very slightly different at 0.7355 kW — the difference is small but can matter for precise specification matching. Use the "Horsepower Type" selector above the input field to switch which figure this calculator uses.
• Treating the converted figure as the final motor selection. A converted value like 11.19 kW is only the unit conversion — it does not by itself determine the correct replacement motor. Select the next suitable standard rating only after checking load torque, duty, speed, starting requirements, service conditions, and the manufacturer's rating table.
• Ignoring duty cycle and ambient conditions. A converted power rating assumes continuous duty at standard ambient temperature; motors used intermittently or in hot environments may need a rating with additional margin beyond the raw converted figure.

Quick Reference: Common HP to kW Conversions

Figures rounded to 2 decimal places using the standard 0.746 conversion factor.

HP to kW Quick Reference Table (1-100 HP)

Full HP-to-kW lookup at the standard 0.746 conversion factor, covering every whole HP value from 1 to 100 — a quick lookup without running the calculator above for a common integer horsepower rating.

Standard Motor Nameplate HP to kW Table (Fractional / Half-Step Sizes)

Most sub-15 HP motor, pump, and fan nameplates aren't rated in whole HP steps — half-HP and fractional sizes like 0.5 HP, 1.5 HP, 5.5 HP, and 7.5 HP are the actual sizes manufacturers sell. This table covers those in-between nameplate ratings that the whole-number table above skips. The third column is an illustrative comparison, not a motor-selection recommendation — it is not necessarily the rating you should buy.

The "Illustrative IEC-style Motor Rating" column shows a commonly available IEC motor rating close to the converted value, for illustration only — it is not a motor-selection recommendation, not a universal or mandatory rating, and actual availability varies by manufacturer. Always verify against the manufacturer's own rating table and the driven load's requirements before selecting a motor.

kW to HP Quick Reference Table (1-100 kW)

The reverse conversion at the same 0.746 factor, covering every whole kW value from 1 to 100 — handy for reading a kW-rated motor or generator nameplate straight across to its equivalent horsepower.

Standard Motor Nameplate kW to HP Table

The reverse lookup for real IEC nameplate kW ratings — the fixed catalogue sizes (0.37 kW, 0.55 kW, 1.5 kW, 5.5 kW, 7.5 kW, and so on) that motors are actually manufactured in, rather than arbitrary whole kilowatt steps.

Motor Efficiency: Why Shaft kW and Input kW Differ

Motor efficiency is the ratio of useful mechanical shaft output to the total electrical power drawn from the supply, expressed as a percentage. A motor rated at 90% efficiency delivering 10 kW at the shaft is actually drawing about 11.1 kW of electrical input power, with the remaining ~1.1 kW dissipated as heat in the windings, core, friction, and windage losses. Typical efficiency varies widely with motor size, design, efficiency class, and operating load point, so the figures below are illustrative tendencies, not fixed guarantees: efficiency generally improves with motor size — small sub-1 kW motors often run 70–80% efficient, while large industrial motors above 50 kW can exceed 94–96% in premium efficiency (IE3/IE4) classes. Always check the specific motor's nameplate or datasheet for its actual rated efficiency. This matters for two very practical reasons: it determines the true electrical demand a motor places on the supply (and therefore the correct cable and breaker size), and it directly affects running cost, since a less efficient motor consumes more electricity for the same mechanical work over its operating life.

HP vs BHP vs kW: What's the Difference?

HP and kW are units of power — 0.746 kW per mechanical HP by this calculator's default definition. BHP (Brake Horsepower) is not a separate unit but a rating terminology: it means power measured at the output shaft using a brake dynamometer or an equivalent method, after internal friction losses. On a motor nameplate, HP or kW ratings almost always already represent this same delivered shaft power, so BHP and nameplate kW typically describe the same physical quantity — just labeled differently depending on the manufacturer's documentation.

Illustrative IEC Motor Rating and Frame Examples

Standard industrial motors are manufactured in fixed size steps rather than arbitrary ratings. The table below is an illustrative example of commonly available standard motor ratings and their typical frame association for a four-pole (1450 rpm) induction motor — it is not a substitute for checking a manufacturer's actual rating table when selecting a replacement motor.

These figures are illustrative examples only. Frame size depends on manufacturer, pole count, mounting arrangement, and design — always confirm against the specific manufacturer's catalogue before specifying or ordering a motor.

IEC vs NEMA Motor Standards

Motors built to different regional standards express and round their power ratings differently, which is a common source of confusion when matching equipment across regions. IEC (International Electrotechnical Commission) standards, used across most of Europe, Asia, and India, rate motors directly in kW with standard steps such as 0.75, 1.1, 1.5, 2.2, 3, 4, 5.5, 7.5, 11, 15, 18.5, 22, and 30 kW. NEMA (National Electrical Manufacturers Association) standards, used predominantly in North America, rate motors in HP with standard steps such as 1, 1.5, 2, 3, 5, 7.5, 10, 15, 20, 25, 30, 40, and 50 HP. Beyond the unit difference, IEC and NEMA motors also differ in frame dimensions and mounting standards. Applications commonly differ in nominal voltage and frequency by region too — 50 Hz is common in IEC markets and 60 Hz in North America — but this is a regional tendency, not a rule intrinsic to either standard, since IEC motors can be built for 60 Hz and NEMA motors for 50 Hz applications; frequency must always be verified from the actual nameplate. So a straightforward HP-to-kW conversion gets you the right power figure, but physically swapping an IEC motor for a NEMA one (or vice versa) also requires checking frame size, shaft dimensions, and supply frequency compatibility.

Mechanical HP vs Metric HP vs Boiler HP

Not all "horsepower" figures mean the same thing. Mechanical (imperial) HP, the most common in motor nameplates, equals 745.7 watts and is what this calculator converts by default. Metric HP (PS/CV), common on older European and some Indian equipment, equals 735.5 watts — a small but real difference (about 1.4%) that matters for precise industrial conversions. Boiler HP is an entirely different, much larger unit (about 9,809 watts) used to rate steam boiler output, not motor shaft power, and should never be confused with mechanical or metric HP when specifying equipment. Always check which HP convention a nameplate or datasheet is using before converting, especially on older or imported equipment.

Boiler HP vs Mechanical HP

Boiler horsepower is a rating used specifically for steam boiler output — it describes the rate of steam generation, not a motor's mechanical shaft power. 1 boiler HP ≈ 9.8095 kW, more than 13 times larger than 1 mechanical HP. Boiler horsepower is not equivalent to mechanical horsepower and should not be used with the standard 0.7457 kW conversion — using the wrong factor on a boiler-rated figure will overstate the equivalent kW by more than 13×. If a nameplate or datasheet specifies "BHP" in a steam or boiler context, confirm it means boiler horsepower before converting, since the abbreviation also overlaps with brake horsepower in motor contexts.

HP to kW for 3-Phase Motors

The HP-to-kW conversion itself does not change because a motor is single-phase or three-phase — a 7.5 HP motor converts to 5.6 kW (7.5 × 0.7457) whether it's wired for single-phase or three-phase supply. What differs between single-phase and three-phase motors is how the electrical input current is calculated from that power figure, since three-phase power distributes the same load across three conductors using a different current formula than single-phase. In short: three-phase affects the current calculation, not the HP-to-kW unit conversion. For finding input current from a shaft power rating, see the kW to Current calculator, which accounts for voltage, phase, and power factor separately.