Power Unit Converter
Convert between watts, kilowatts, megawatts, metric horsepower, BTU/hour and calories/second — all at once, live.
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How It's Calculated
Power conversion is a set of fixed multipliers against the SI base unit, the watt: 1 kW = 1,000 W, 1 MW = 1,000,000 W, 1 metric horsepower (PS/CV) = 735.5 W, 1 mechanical/imperial horsepower (HP) = 745.7 W, 1 BTU/h ≈ 0.293 W (or 1 W ≈ 3.412 BTU/h), and 1 calorie/second ≈ 4.184 W. Enter a value in any field and the rest recompute from the same underlying watt figure.
Worked example — a car advertised at "150 PS": 150 × 735.5 W = 110,325 W ≈ 110.3 kW. Convert that same engine to imperial horsepower instead of watts: 110,325 W ÷ 745.7 W/HP ≈ 147.9 HP — noticeably lower than "150" even though it is the same physical engine, purely because PS and HP are different-sized units. This ~1.4% gap is exactly why a car specced at "150 PS" in Europe is often listed as "148 HP" in the US.
What to Know
- There are two different "horsepower" units, and they get mixed up constantly. Metric horsepower (PS, CV, hk — used across most of Europe, Japan and elsewhere) equals 735.5 W; mechanical/imperial horsepower (HP — the US standard) equals 745.7 W. The difference is small (~1.4%) but real, and manufacturer spec sheets don't always say which one they mean.
- BTU/h measures heating and cooling capacity, not general power — it is the unit air conditioners and furnaces are rated in. 1 watt ≈ 3.412 BTU/h, so a 3,500 W electric heater outputs roughly 11,942 BTU/h.
- Watts, kilowatts and megawatts are exact SI multiples — no ambiguity there. The ambiguity only enters with horsepower (which definition?) and with older thermal/calorie-based units, which historically had slightly different definitions (thermochemical vs. international calorie) though the difference is negligible for everyday conversions.
- Power is not the same as energy. Watts describe the rate energy is used or produced at a given instant; kilowatt-hours, joules and BTUs (total, not per hour) describe an amount of energy accumulated over time. Confusing the two — for example reading a "3 kW" appliance rating as if it were "3 kWh of usage" — is one of the most common mistakes when reading appliance labels or utility bills.
- For the same physical engine or motor, expect small numeric differences between specification sheets from different regions purely because of which horsepower or power unit convention was used — that is a labeling difference, not a performance difference.
Frequently Asked Questions
Which horsepower definition is used?
Metric horsepower (PS/CV, 735.49875 W) — the definition used across most of the world outside the US. Mechanical (imperial) horsepower is very close at 745.7 W, a roughly 1.4% difference.
Why do a car's PS and HP figures differ even though it's the same engine?
Because PS (metric horsepower, 735.5 W) and HP (mechanical/imperial horsepower, 745.7 W) are different-sized units for the same physical quantity, power. A 150 PS engine is about 147.9 HP — roughly 1.4% lower purely from the unit definition, not the engine itself.
How does BTU/h relate to watts?
1 watt ≈ 3.412 BTU/h, and 1 BTU/h ≈ 0.293 W. BTU/h is the standard unit for air conditioner and heater capacity in the US; a "12,000 BTU" mini-split is roughly 3,517 W (about 1 ton of cooling in HVAC terms).
What is a kilowatt in horsepower?
1 kW ≈ 1.341 mechanical horsepower or ≈ 1.360 metric horsepower. A 100 kW electric motor is therefore roughly 134 HP (mechanical) or 136 PS (metric) — close but not identical figures depending on which horsepower standard is quoted.
Why does my electricity bill use kWh instead of watts?
A kilowatt-hour is a unit of energy (power × time), not power itself — it measures how much work was done over an hour, e.g. a 1,000 W appliance running for 1 hour uses 1 kWh. This converter handles instantaneous power units; energy units like kWh or joules require multiplying by a duration.
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