Power Converter

Q: What is the difference between watts, kilowatts, and horsepower?

All three measure power, which is the rate at which energy is transferred or work is performed. Watts are the SI unit of power, where 1 watt equals 1 joule of energy transferred per second. A kilowatt is 1000 watts. Horsepower is a non-SI unit that is approximately equal to 745.7 watts in the mechanical definition. Watts and kilowatts are commonly used for electrical systems and modern engineering, while horsepower is still widely used for engines, motors, and machinery, especially in automotive contexts.

Q: Why are there five different types of horsepower?

Horsepower began as a historical unit for comparing engine output to horse-drawn work, but different countries and industries defined it differently over time. The main variants are mechanical horsepower, metric horsepower, electric horsepower, UK horsepower, and boiler horsepower. Mechanical horsepower is about 745.7 watts and is common in US and UK automotive contexts. Metric horsepower is about 735.5 watts and is often used in Europe under labels such as PS or CV. Electric horsepower is defined as exactly 746 watts. Boiler horsepower is a much larger historical unit used for steam boiler capacity. For accurate comparison, it is important to know which horsepower definition is being used.

Q: How do I convert horsepower to kilowatts?

To convert horsepower to kilowatts, multiply the horsepower value by its watt equivalent and divide by 1000. For mechanical horsepower, the formula is kW = hp × 0.7457. For metric horsepower, the formula is kW = PS × 0.7355. For example, 150 mechanical horsepower equals 111.9 kilowatts, while 150 metric horsepower equals 110.3 kilowatts. The converter handles these variations automatically when you choose the correct horsepower type.

Q: What is BTU per hour and how does it relate to watts?

BTU per hour, written as BTU/h, is a thermal power unit commonly used in US heating and cooling specifications. It measures the rate of energy transfer in British Thermal Units per hour. One BTU per hour is approximately equal to 0.293 watts, and 1 kilowatt is approximately equal to 3412 BTU per hour. This is why air conditioner capacity in the United States is often given in BTU per hour, while European specifications more often use kilowatts directly.

Q: What is the difference between power and energy?

Power is the rate at which energy is transferred, and it is measured in units such as watts, kilowatts, or horsepower. Energy is the total amount transferred or used over time, and it is measured in units such as watt-hours, kilowatt-hours, joules, or BTUs as an energy unit. For example, a device rated at 2 kilowatts is describing power. If that device runs for 5 hours, it uses 10 kilowatt-hours of energy. This converter handles power units, not energy units.

Q: Which horsepower type should I use for a car specification?

It depends on the market. US-market vehicles typically use mechanical horsepower. European vehicles often use kilowatts and may also show metric horsepower such as PS or CV. UK-market vehicles often use bhp, which is functionally equivalent to mechanical horsepower in common automotive use. When comparing cars from different regions, converting both values to kilowatts is the clearest way to make a direct comparison.

Q: Can I convert milliwatts to horsepower?

Yes. The converter supports milliwatts as both a source and destination unit, including conversion to all supported horsepower types. For reference, 1 mechanical horsepower equals 745700 milliwatts. While this conversion is mathematically valid, it is usually only practical in specialized technical contexts because milliwatts are used for very small power levels such as sensors and electronic components.

Convert power units instantly—Watts (W), Kilowatts (kW), Megawatts (MW), Horsepower (hp) and more. Enter a value, choose units, and get accurate conversions in seconds. Ideal for engineering, HVAC, vehicles, and energy calculations. Free and easy to use.

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Power Converter

The Power Converter converts power values between 20 units spanning SI metric units, five horsepower variants, thermal and BTU-based units, and legacy engineering units. Select the source unit and the target unit, enter the value, and click Convert. The result is displayed immediately.

Power units vary by industry, geography, and era. Electrical engineers work in watts and kilowatts; automotive engineers use horsepower (with different definitions in the US and Europe); HVAC professionals use BTU per hour; physicists may encounter ergs per second. This converter handles all of them accurately in one place.

How to use the Power Converter

Enter the power value you want to convert in the input field.
Select the From unit — the unit your value is currently in.
Select the To unit — the unit you want to convert to.
Click Convert. The result appears immediately.
To convert between additional unit pairs, change the From or To dropdown and click Convert again — the entered value is retained.

All 20 units — conversion factors and typical contexts

The table below shows every supported unit, its value in watts (the SI base unit of power), and the context in which it is typically used:

Unit	In watts (W)	Typical context
SI / metric units
Milliwatt (mW)	0.001 W	Electronic components, RF signal power, low-power sensors and IoT devices. A smartphone on standby may consume 10–100 mW.
Watt (W)	1 W	The SI base unit of power. Light bulbs, small appliances, USB charging. A standard LED bulb is typically 8–15 W; a laptop charger 45–100 W.
Kilowatt (kW)	1,000 W	Electric motors, HVAC systems, electric vehicle chargers, home energy consumption. A typical UK household uses 3–5 kW peak; an EV home charger is 7–22 kW.
Megawatt (MW)	1,000,000 W	Power stations, industrial generation, offshore wind turbines. A typical offshore wind turbine is 5–15 MW; a small gas peaker plant may be 20–100 MW.
Horsepower variants
Horsepower (550 ft·lbf/s) — mechanical / imperial	745.7 W	The original mechanical horsepower definition (James Watt, 18th century): power to lift 550 foot-pounds per second. Used for internal combustion engines in the US market. When a car manufacturer states 'horsepower' without qualification, this is usually the intended definition.
Horsepower (metric)	735.5 W	The European/metric horsepower definition: power to lift 75 kilogram-meters per second (= 75 kgf·m/s). Used for engine ratings in European markets. Slightly lower than mechanical hp. German PS (Pferdestärke) and French CV use this definition. 1 PS = 1 CV ≈ 0.986 mechanical hp.
Horsepower (electric)	746.0 W	Exactly 746 W. Used for rating electric motors in the United States. Defined by the US National Electrical Manufacturers Association (NEMA). Very close to mechanical hp (745.7 W) but not identical.
Horsepower (UK)	745.7 W	The British imperial horsepower, defined identically to the mechanical/550 ft·lbf/s definition. Used in UK-market vehicle and machinery specifications. Equivalent to mechanical hp for practical purposes.
Horsepower (boiler)	9,810.7 W	A historical unit used to rate steam boilers: the power required to evaporate 34.5 pounds of water per hour at 212°F. Approximately 13.15 mechanical horsepower. Still encountered in legacy industrial boiler documentation and some US commercial/industrial specifications.
Thermal and caloric units
BTU (thermochemical)/hour	0.2929 W	US HVAC industry standard for air conditioner and heating equipment capacity. A 12,000 BTU/h unit is commonly called '1 ton of cooling'. A typical UK domestic boiler is 18,000–36,000 BTU/h (5.3–10.5 kW).
BTU (SI)/hour	0.2931 W	The International Standard BTU definition. Slightly different from the thermochemical BTU. Most HVAC specifications use the thermochemical BTU; always verify which definition applies for precision engineering work.
Foot-pound force/second	1.356 W	Imperial mechanical power unit: 1 ft·lbf/s = 1/550 mechanical horsepower. Used in some US engineering calculations for mechanical systems.
Erg/second	0.0000001 W	CGS (centimeter-gram-second) unit of power. Encountered in older physics literature and some scientific instruments. 1 W = 10 million erg/s. Rarely used in modern engineering.

Power vs energy — an important distinction

Power and energy are different physical quantities and use different units. Power is the rate of energy transfer — how many joules per second (watts). Energy is the total amount transferred over time — watt-hours (Wh), kilowatt-hours (kWh), BTUs (as a thermal energy unit), or joules. An appliance rated at 2 kW running for 3 hours uses 6 kWh of energy. Watts measure a rate; watt-hours measure a total. This converter handles power units only. If you need energy units (Wh, kWh, BTU as energy, joules), look for a dedicated energy converter.

The five horsepower types — why they differ

Horsepower is one of the most confusing units in engineering because multiple different definitions exist, each with a slightly different watt equivalent. Using the wrong variant introduces a small but real error in specifications and comparisons:

Mechanical horsepower (550 ft·lbf/s) = 745.699 W. The original definition. Used for internal combustion engine ratings in the US and UK automotive market. When a US car spec sheet says 'horsepower', this definition applies. Also called imperial horsepower.
Metric horsepower (PS / CV) = 735.499 W. Used for European engine ratings. German 'PS' (Pferdestärke) and French 'CV' (Cheval Vapeur) are the same unit. 100 PS = 98.6 mechanical hp. A car rated at 200 PS has slightly less power than one rated at 200 mechanical hp.
Electric horsepower = 746.0 W exactly. Used to rate electric motors in the US under NEMA standards. Defined as exactly 746 W. Very close to mechanical hp but not identical.
UK horsepower = 745.7 W. Defined identically to mechanical horsepower. Used in UK machinery and vehicle specifications. Numerically equivalent to mechanical hp.
Boiler horsepower = 9,810.657 W. A historical unit for steam boiler capacity — the power to evaporate 34.5 lb of water per hour at 212°F. Approximately 13.15 mechanical horsepower. Rarely used outside legacy industrial boiler documentation.

For vehicle comparisons, always confirm which horsepower definition is being used. A European car listed at 150 PS and a US car listed at 150 hp have almost the same power — but not quite: 150 PS = 150 × 735.5 = 110.3 kW; 150 hp (mechanical) = 150 × 745.7 = 111.9 kW. For direct comparison, convert both to kilowatts. The metric and mechanical horsepower difference is approximately 1.4% — small but relevant for precise engineering specifications.

Common use cases by industry

Context	Common conversion	Notes
Vehicle and engine specifications	hp (mechanical or metric) ↔ kW	European car specifications list power in kW; US and UK specifications typically list in bhp (brake horsepower, equivalent to mechanical hp). 100 kW ≈ 134 mechanical hp ≈ 136 metric hp. Check which hp standard applies before comparing across markets.
Domestic appliances and electronics	W ↔ kW	Appliance labels in watts; energy bills in kilowatt-hours (kWh). A 1,000 W (1 kW) appliance running for one hour uses 1 kWh. Power (kW) × time (hours) = energy (kWh).
HVAC and air conditioning	BTU/h ↔ kW	US HVAC capacity in BTU/h; European specifications in kW. 1 kW ≈ 3,412 BTU/h. A 12,000 BTU/h air conditioner is approximately 3.5 kW. Boiler capacity in the UK is typically stated in kW.
Industrial motors and generators	kW ↔ hp (electric)	US-market motors rated in hp (electric, 746 W each); international motors in kW. Motor nameplates often show both. Check the motor's nameplate for rated power, efficiency, and whether the value is input power or mechanical output power.
Solar and wind energy systems	kW ↔ MW	Residential solar panels: typically rated 5–15 kW peak. Commercial systems: hundreds of kW to tens of MW. Grid-scale wind turbines: 3–15 MW. Energy output (kWh or MWh) requires multiplying power by hours of generation.
Physics and engineering coursework	Various ↔ W	Convert all values to watts for consistent calculations. 1 mechanical hp = 745.7 W. 1 BTU/h = 0.293 W. 1 erg/s = 10⁻⁷ W. Always confirm which horsepower definition applies in textbook problems — mechanical (745.7 W) and metric (735.5 W) are not the same.

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Frequently asked questions

What is the difference between watts, kilowatts, and horsepower?

All three measure power — the rate at which energy is transferred or work is performed. Watts (W) are the SI unit of power; 1 watt = 1 joule of energy transferred per second. A kilowatt (kW) is 1,000 watts. Horsepower (hp) is a non-SI unit approximately equal to 745.7 watts (mechanical definition). The units differ in scale and origin: watts and kilowatts are used for electrical systems and most modern engineering; horsepower is used for engines, motors, and some machinery, particularly in automotive contexts.

Why are there five different types of horsepower?

Horsepower originated as a unit to compare steam engine output to horse-drawn work in the 18th century, but different industries and countries defined it differently over time. The five variants are: mechanical (745.7 W, US/UK automotive and general engineering), metric (735.5 W, European PS/CV for vehicles), electric (746 W exactly, US electric motors per NEMA), UK (745.7 W, British machinery — identical to mechanical), and boiler (9,810 W, historical steam boiler capacity). For precise engineering work, always specify which horsepower type applies. For vehicle comparisons across markets, convert to kilowatts.

How do I convert horsepower to kilowatts?

Multiply the horsepower value by the watt equivalent and divide by 1,000. For mechanical hp: kW = hp × 0.7457. For metric hp (PS): kW = PS × 0.7355. Examples: 150 mechanical hp = 150 × 0.7457 = 111.9 kW. 150 metric hp (PS) = 150 × 0.7355 = 110.3 kW. The converter handles all five horsepower types accurately — select the correct 'From' unit for your source specification.

What is BTU per hour and how does it relate to watts?

BTU/h (British Thermal Units per hour) is a thermal power unit widely used in US HVAC specifications. One BTU is the energy required to raise one pound of water by 1°F; BTU/h is the rate of energy transfer in BTUs per hour. 1 BTU (thermochemical)/h ≈ 0.293 W, or equivalently 1 kW ≈ 3,412 BTU/h. Air conditioner capacity is commonly stated in BTU/h in the US — a 12,000 BTU/h unit equals approximately 3.5 kW of cooling capacity. European HVAC specifications use kW directly.

What is the difference between power and energy?

Power is the rate of energy transfer — measured in watts, kilowatts, or horsepower. Energy is the total amount of work done or transferred over a period of time — measured in watt-hours (Wh), kilowatt-hours (kWh), joules, or BTUs as an energy unit. An appliance rated at 2 kW (power) running for 5 hours uses 10 kWh (energy). This converter converts power units. Energy units (kWh, BTU as energy, joules) require a separate energy unit converter.

Which horsepower type should I use for a car specification?

It depends on the market. US-market cars list power in mechanical horsepower (hp, 745.7 W each). European-market cars list power in kilowatts (kW) and often also in metric horsepower (PS or CV, 735.5 W each). UK-market cars list power in bhp (brake horsepower) — functionally equivalent to mechanical hp. To compare a US-market and European-market car directly, convert both to kilowatts using the appropriate horsepower definition (mechanical or metric). A car listed at '200 hp' in the US has approximately 149.1 kW; a car listed at '200 PS' in Germany has approximately 147.1 kW.

Can I convert milliwatts to horsepower?

Yes — the converter supports milliwatts as a From or To unit and can convert to any other supported unit including all horsepower types. For context: 1 mechanical horsepower = 745,700 milliwatts. Most milliwatt values represent very small power — electronic components, sensors, and low-power devices — so conversion to horsepower is rarely practically meaningful, but it is mathematically valid and the converter handles it correctly.

Is the Power Converter free?

Yes. The converter is free within the daily usage limits shown above. Guest users can perform 25 conversions per day without creating an account. Registering a free ToolsPiNG account increases the daily limit to 100 conversions per day.