Power Unit Converter

Convert between watts, kilowatts, megawatts, and gigawatts — plus the three flavours of horsepower (mechanical 745.70 W, electrical 746 W, metric PS 735.50 W), BTU/h and BTU/min for North American heat-rate, ft·lb/s for mechanical work-rate, and the CGS / thermochemical forms (erg/s, cal/s, kcal/h). 15 units, NIST SP 811 factors, round-trip stable. Type a value, pick a source unit, see every other unit at the same instant. Nothing leaves your browser.

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About the units

W, kW, MW, GW — SI prefixes of the watt. The watt is a rate of one joule per second.
hp (mechanical) — the imperial mechanical horsepower used in the auto and pump industries, 1 hp(I) = 745.6998715822702 W exactly (NIST SP 811).
hp(E) (electrical) — the IEEE / IEC rating, 1 hp(E) = 746 W exactly.
PS (German Pferdestärke) — metric horsepower, 1 PS = 735.49875 W exactly. Used on European car spec sheets.
BTU/h — British thermal units per hour, 1 BTU/h = 0.29307107017 W. The standard North American heat-rate (HVAC, furnace output).
ft·lb/s — foot-pound-force per second, 1 ft·lb/s = 1.3558179483314004 W. Mechanical work-rate.
cal/s, kcal/h — calories per second / kilocalories per hour. Thermochemical (1 cal = 4.184 J).
erg/s — CGS unit, 1 erg/s = 1e-7 W.

Not shipped: shaft (brake) vs indicated horsepower, dBm / dBW (those are power ratios referenced to 1 mW / 1 W), and tons of refrigeration. Conversion is round-trip stable to within 1 ULP of IEEE-754 precision.