All Power Units

How to Convert Power Units?

Power measures the rate at which energy is transferred or converted. This converter uses standard conversion factors to instantly convert between watts, kilowatts, megawatts, horsepower, BTU per hour, and foot-pounds per second.

Simply enter a value, select your source unit, and choose the target unit. The converter calculates all unit equivalents simultaneously, showing you the complete conversion table.

Frequently Asked Questions

What units of power does this converter handle?

This converter handles the SI watt and its standard prefixed forms (microwatt, milliwatt, watt, kilowatt, megawatt, gigawatt), the horsepower family (mechanical/imperial HP, metric PS, electrical HP), BTU per hour for HVAC, calories per second for biology/chemistry, and foot-pounds per second for legacy engineering. The watt is the SI derived unit of power, defined as 1 joule per second or equivalently 1 V*A. All metric-prefixed watt conversions are exact powers of ten. The horsepower variations differ by definition: mechanical HP = 745.6998715822702 W, metric horsepower (PS, CV, ch) = 735.49875 W, electrical HP = 746 W. Always specify which 'HP' you mean in engineering documents.

What are the exact conversion factors for power?

1 kW = exactly 1000 W. 1 mechanical horsepower (HP) = 550 ft*lbf/s = exactly 745.6998715822702 W. 1 metric horsepower (PS, CV) = 75 kgf*m/s = exactly 735.49875 W (using 1 kgf = 9.80665 N). 1 BTU/h = exactly 1055.05585262 J/3600 s = 0.29307107017222... W. 1 ton of refrigeration = exactly 12,000 BTU/h = 3.5168528 kW. 1 cal/s (thermochemical calorie) = 4.184 W exactly. 1 ft*lbf/s = exactly 1.3558179483314004 W. These factors are exact rational numbers derived from the international yard/pound and the joule definitions; the only rounding error comes from final decimal display.

When should I use W, kW, HP, BTU/h, or PS?

Use watts (W) for electronics, LED bulbs, small motors, audio amplifiers (where ratings are RMS watts). Use kilowatts (kW) for car engines (modern), home appliances, water heaters, and electric motors above 1 kW. Use megawatts (MW) for power plant output, large industrial facilities, and aviation engines. Use horsepower (HP) for car/truck engines in US markets (still dominant in marketing despite kW becoming standard in EU), boat motors, and traditional industrial machinery. Use metric horsepower (PS, CV, ch) in Europe, Japan, and Latin America for cars. Use BTU/h for HVAC sizing in the US (air conditioners, furnaces, heat pumps) and ton-of-refrigeration for chillers. Use cal/s for metabolic rates and chemical reaction rates.

How precise are the conversions and what about rated vs peak?

Internally the tool uses 64-bit floating-point and the exact factors above, giving 15+ significant digits of precision. In practice, power ratings rarely justify more than 3 to 4 significant figures. Engine HP ratings vary by measurement method: SAE gross (before accessories), SAE net (with all accessories), DIN (European, similar to SAE net), and JIS (Japanese, slightly different). Continuous-duty vs peak-duty: a motor 'rated 5 kW' may briefly produce 7 to 10 kW. Inverter air conditioners specify cooling capacity in BTU/h or kW, but electrical input is typically 1/3 to 1/4 of that (COP/EER ratings). The converter is pure unit math; the engineering definition behind the number is your responsibility.

What are the common gotchas in power conversion?

First, mechanical HP vs metric HP differ by 1.39%: 100 mechanical HP = 101.4 metric PS. Marketing often blurs this. Second, watts (real power) vs volt-amperes (apparent power): in AC circuits, S [VA] = V*I but P [W] = V*I*cos(phi); for a power factor of 0.8, a 1 kW heater draws 1.25 kVA from the grid. UPS units are rated in VA, not W. Third, 'cooling tons' for HVAC: 1 ton = 12,000 BTU/h = removing the heat needed to freeze 1 short ton of water in 24 h. Fourth, BTU vs BTU per hour: BTU is energy (a joule cousin), BTU/h is power; advertising frequently drops the '/h' incorrectly. Fifth, 'continuous' vs 'surge' power on power supplies and batteries can differ 2x.

What is the relationship between power, energy, torque, and force?

Power is the rate of energy transfer: P = dE/dt, with E in joules and t in seconds, giving watts. So 1 kWh of energy at 1 hour delivery equals 1 kW of power. Power equals force times velocity for translation: P = F*v with F in newtons and v in m/s. Power equals torque times angular velocity for rotation: P = T*omega with T in N*m and omega in rad/s. A car engine producing 300 N*m of torque at 6000 rpm delivers 300 * 2*pi*6000/60 = 188.5 kW = 253 mechanical HP. The converter handles unit conversion only; deriving power from torque or force requires the additional rotational or translational variable.

How is the watt defined in the modern SI system?

The watt is an SI coherent derived unit: 1 W = 1 J/s = 1 kg*m^2/s^3 = 1 V*A. After the 2019 SI redefinition, all four base units involved (kg, m, s, A) are defined via fixed fundamental constants: kilogram by Planck constant h = 6.62607015 x 10^-34 J*s, meter by speed of light c = 299,792,458 m/s, second by caesium frequency, ampere by elementary charge e = 1.602176634 x 10^-19 C. The watt therefore inherits exact definitional precision. The Kibble (watt) balance is the primary realization of the kilogram via electrical power, and indirectly anchors the watt at the highest accuracy. The BIPM and NMIs coordinate global metrology.

What are edge cases at extreme power scales?

Very low power: a wristwatch consumes ~1 uW, a single human neuron firing ~10^-12 W, a typical cell phone idle ~50 mW. Human metabolic power averages ~100 W (basal) up to 1000 W (intense exercise). Domestic power: kettle 2 kW, household peak load 10 kW, car engine 100 kW, electric truck 500 kW. Industrial: large turbine 1 GW, world power plant capacity 7 TW (continuous average), total solar irradiance reaching Earth 174 PW (174 x 10^15 W). At cosmic scales: Sun's total output 3.85 x 10^26 W, brightest stars 10^32 W, galaxy 10^36 W. The converter handles 10^-18 W to 10^40 W mathematically, though units beyond TW are rarely useful day-to-day.

Units

Watt (W)

The watt is the SI unit of power, defined as one joule per second. It's used universally in electrical applications, from small electronics (smartphone chargers use 5-20W) to household appliances (microwave ovens use 700-1200W).

Kilowatt (kW)

Equal to 1,000 watts, the kilowatt is commonly used to express the power of electric motors, heating systems, and home energy consumption. A typical home uses 1-2 kW on average, while electric vehicles charge at 7-22 kW.

Megawatt (MW)

Equal to 1,000,000 watts, the megawatt measures large-scale power generation. A single wind turbine produces 2-3 MW, while nuclear power plants generate 500-1,500 MW per reactor.

Horsepower (hp)

Originally defined by James Watt to compare steam engines to draft horses, one mechanical horsepower equals approximately 745.7 watts. It remains the standard unit for rating car engines, with typical vehicles ranging from 100-400 hp.

BTU per Hour (BTU/h)

The British Thermal Unit per hour measures heating and cooling capacity in HVAC systems. Air conditioners are rated in BTU/h, with window units typically providing 5,000-25,000 BTU/h depending on room size.

Common Power Conversions