Power Unit Converter
Convert between any pair of power units — watts, kilowatts, megawatts, mechanical horsepower, metric horsepower (PS), BTU per hour, and more — using conversion factors verified against NIST and BIPM references. Type a value and the result updates instantly.
Reviewed by WuTools Engineering Team · Last updated
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What is power, and why are there so many units?
Power is the rate at which energy is transferred or work is done — joules of energy per second. The SI unit is the watt (W), defined as 1 joule per second. The same physical quantity describes a 60-watt lamp's light output, a 1500-watt kettle's heating, a 75 kW car engine, a 1 GW nuclear reactor, and the milliwatts that come out of a Wi-Fi antenna. Whenever there is energy moving in time, power is the right number.
The reason there are so many power units is that engineering disciplines locked in their conventions before the SI watt could displace them. Car salesmen still quote horsepower because James Watt sold his steam engines that way in 1782. American HVAC engineers measure air conditioners in BTU per hour because heating loads were defined that way in colonial times. European car ratings use 'metric horsepower' (PS / CV / cv), a unit different from US mechanical horsepower by 1.4%. Each industry's training, regulations, and supply chain stuck — and the units stuck with them.
The power units, explained
Watt (W) and its multiples — the SI baseline
1 W = 1 J/s = 1 N·m/s. The watt is named after James Watt and is the coherent SI unit. The kilowatt (kW, 10³ W) covers most household appliances and small motors; the megawatt (MW, 10⁶ W) describes industrial drives and small power plants; the gigawatt (GW, 10⁹ W) is the scale of nuclear reactors and large hydroelectric stations. The milliwatt (mW, 10⁻³ W) measures laser pointers and radio transmit power.
Mechanical horsepower (hp) — the imperial workhorse
1 mechanical horsepower equals 550 ft·lbf/s = 745.6998715822702 W exactly. James Watt defined it in 1782 by observing pit ponies lifting coal; he wanted a unit that let mine owners compare his steam engines to the horses they replaced. Today it survives in US car ratings, lawn-mower specs, US-spec marine outboards, and any imperial machinery. 'Brake horsepower' (BHP) is mechanical horsepower measured at the crankshaft on a dynamometer.
Metric horsepower (PS, CV, cv) — the European car standard
Metric horsepower is defined as the power needed to lift 75 kgf one meter in one second, which is 75 × 9.80665 = 735.49875 W exactly. It is 1.4% smaller than mechanical horsepower. Germany calls it Pferdestärke (PS), Spain caballo de vapor (CV), Italy cavallo vapore (cv), France cheval-vapeur (ch), and Japan 馬力 (bariki). Most European, Japanese, and Korean car catalogs list power in PS, then convert to kW for the EU technical sheet.
BTU per hour (BTU/h) — air conditioning and heating
1 BTU/h ≈ 0.29307107017 W. The BTU (British thermal unit) is the energy needed to raise one pound of water by 1 °F. Air-conditioner capacity is rated in BTU/h in the US: a 9000 BTU/h unit cools a small bedroom (≈2.6 kW), a 12 000 BTU/h unit a living room (≈3.5 kW = 1 ton of refrigeration). Boiler and furnace output is similarly in BTU/h. The unit is enshrined in HVAC training, building codes, and equipment labels.
Foot-pound per second (ft·lbf/s) — engineering
1 ft·lbf/s = 1.3558179483314004 W. This is the imperial coherent unit of power, derived from foot-pounds of work per second. It is rare in everyday life — most engineering calculations divide by 550 to convert to mechanical horsepower — but it appears in mechanical engineering textbooks and some legacy machinery specifications.
Larger and smaller scales (GW, MW, mW)
Scale matters. A typical incandescent bulb is 60 W, an LED bulb 9 W, a phone charger 5–20 W. A microwave oven is around 1000 W; an electric kettle 2000–3000 W. A house draws ~1–3 kW average, with peaks above 10 kW. A small car engine is ~75 kW, a Tesla supercharger 250 kW. A wind turbine produces 2–8 MW. A modern nuclear reactor outputs 1.0–1.6 GW electrical.
Real-world applications and which unit to expect
- Car engines: American spec sheets use mechanical horsepower (hp). European, Japanese, and Korean catalogs use metric horsepower (PS / CV / cv). EU type approval requires kW. A 200 hp engine equals 149.1 kW = 202.7 PS. Dealers usually quote the 'bigger' number — PS for European brands, hp for American.
- Air conditioners: Cooling capacity is rated in BTU/h in the US and Asia, in kW in Europe. Common residential units in Vietnam: 9000 BTU/h (1 hp ~ 2.6 kW for a 12 m² room), 12 000 BTU/h (1.5 hp ~ 3.5 kW for an 18 m² room), 18 000 BTU/h (2 hp ~ 5.3 kW for a 24 m² room). The 'hp' label here is a marketing convention — it is roughly the compressor's mechanical horsepower input, not the cooling output.
- Household appliances: Watts. An LED bulb is 9 W, a desktop computer 80–150 W, a refrigerator 100–300 W average, a hair dryer 1500–2200 W, an electric kettle 1500–3000 W. Total household demand peaks at 5–15 kW depending on size and electric heating.
- Electric motors: Industrial motors are sized in kW (Europe) or hp (US). Common sizes: 0.75 kW (1 hp), 1.5 kW (2 hp), 5.5 kW (7.5 hp), 15 kW (20 hp), 75 kW (100 hp). NEMA frame numbers correlate to hp; IEC frame numbers to kW.
- Power plants and transmission: Generation capacity is in MW or GW. A coal plant 500–800 MW per unit, a wind turbine 2–8 MW, a nuclear reactor 1.0–1.6 GW, a large hydropower dam 5–22 GW. Transmission line ratings are in MW or GVA.
- Audio amplifiers and radio transmitters: Audio amplifiers list output in watts continuous (RMS). Home stereo is 50–100 W per channel; pro PA 1000+ W. RF transmit power is in watts or dBm: 30 dBm = 1 W, 40 dBm = 10 W. Wi-Fi routers transmit at 100 mW (20 dBm).
- Light sources: Lumens measure light output, watts measure electrical input. A 60 W incandescent and a 9 W LED produce roughly the same lumens, but the LED is over 6× more efficient. Modern lamp packaging quotes both.
How much is 1 unit of each in watts?
| Unit | Value in watts (W) |
|---|---|
| 1 W (Watt) | 1 Pa |
| 1 kW (Kilowatt) | 1000 Pa |
| 1 MW (Megawatt) | 1000000 Pa |
| 1 GW (Gigawatt) | 1000000000 Pa |
| 1 mW (Milliwatt) | 0.001 Pa |
| 1 hp (Horsepower (mechanical)) | 745.6998715822702 Pa |
| 1 PS (Metric horsepower (PS)) | 735.49875 Pa |
| 1 BTU/h (BTU per hour) | 0.29307107017 Pa |
| 1 ft·lbf/s (Foot-pound per second) | 1.3558179483314004 Pa |
Frequently asked questions about power units
How do I convert between any two power units?
Multiply by the source unit's watt-factor and divide by the target's. Example: convert 200 hp to kW → 200 × 745.6998 ÷ 1000 = 149.14 kW. The converter above does this in real time.
What is the difference between mechanical hp and metric hp (PS)?
Mechanical horsepower (used in the US) is exactly 745.6998715822702 W, defined as 550 ft·lbf/s. Metric horsepower (PS, CV, cv, used in Europe and Asia) is exactly 735.49875 W, defined as 75 kgf·m/s. Metric hp is 1.4% smaller. So a car rated 100 PS in Europe is 98.6 hp by US measurement, or 73.55 kW.
Why do air conditioners use BTU/h?
Historical inertia. The BTU was defined for heating loads in the British Empire and brought to American HVAC engineering. Building heating and cooling load calculations still use BTU/h in the US, so manufacturers rate equipment to match. A 'one-ton' air conditioner removes 12 000 BTU/h ≈ 3.517 kW — a unit that came from how much heat was absorbed by melting one ton of ice in 24 hours.
What does the 'hp' label on an air conditioner mean?
On split AC units sold in Asia, 'hp' is a marketing shorthand related to the compressor's input power, not the cooling output. The rough rule: 1 hp AC ≈ 9000 BTU/h cooling ≈ 2.6 kW cooling output ≈ 750 W electrical input. The exact relationship varies by efficiency class. Always cross-check the BTU/h or kW rating on the energy label.
What is dBm and how does it relate to watts?
dBm is a logarithmic scale for power referenced to 1 milliwatt: P(dBm) = 10 × log₁₀(P(mW)). 0 dBm = 1 mW, 10 dBm = 10 mW, 20 dBm = 100 mW, 30 dBm = 1 W, 40 dBm = 10 W. RF engineers prefer dBm because gains and losses on signal paths add and subtract in decibels.
Is a kettle's wattage the same as the heat it delivers?
Almost. A 2200 W kettle draws 2200 W of electrical input from the wall and converts nearly all of it into heat in the water (electric resistance heating is ~99% efficient at delivering heat to the water; the small loss is housing convection). A microwave oven is different — a '1000 W microwave' means 1000 W of cooking power; the actual electrical input is ~1500 W because the magnetron is ~67% efficient.
How precise are these conversion factors?
All factors used by this converter are sourced from NIST SP 811 and the BIPM SI Brochure. 1 hp = 745.6998715822702 W, 1 PS = 735.49875 W, and 1 ft·lbf/s = 1.3558179483314004 W are exact by definition. The BTU/h factor depends on which BTU definition is used (this converter uses the IT BTU, the industry standard). Display rounds to ten significant digits.
How much power does a typical household use?
An average US home uses about 1.2 kW continuously (10 500 kWh/year ÷ 8760 h). Peaks during cooking or HVAC startup reach 5–10 kW. Total contracted breaker capacity is usually 100–200 amps × 240 V = 24–48 kW. European households contract 3–11 kVA depending on whether they have electric heating.
Why do EU type-approval documents quote kW for cars?
EU Directive 80/1269/EEC standardised vehicle power measurement and required reporting in kW. National catalogs still publish PS / CV / cv because consumers expect it, but the legal documentation cites kW. ECE R85 specifies the test bench protocol so all manufacturers report comparable numbers.
Can I link to a specific conversion?
Yes. The URL updates as you change units and values, so you can copy the address bar after any conversion. Example: ?from=hp&to=kW&x=200.
References
Dedicated converter pages
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