Power Converter
Convert power units between watts, kilowatts, megawatts, horsepower, BTU/hour, foot-pounds/second, and calories/second.
Power Converter
Calculator
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Formula: Converted = Input x (From Unit in Watts) / (To Unit in Watts)
Worked example โ 250 hp = 186.425 kW = 186,425 W = 253.47 PS
Formula
Converted = Input x (From Unit in Watts) / (To Unit in Watts)
All power units are converted through watts as the base unit. Multiply the input value by its conversion factor to watts, then divide by the target unit factor. For example, 1 horsepower = 745.7 watts, 1 kilowatt = 1000 watts, 1 BTU/h = 0.293 watts.
Worked Examples
Example 1: Engine Power Conversion
Problem:A car engine produces 250 horsepower. Convert to kilowatts and watts.
Solution:Watts = 250 x 745.7 = 186,425 W Kilowatts = 186,425 / 1000 = 186.425 kW Metric HP = 186,425 / 735.5 = 253.47 PS
Result:250 hp = 186.425 kW = 186,425 W = 253.47 PS
Example 2: HVAC Power Rating
Problem:An air conditioner is rated at 12,000 BTU/h. What is its power in watts and kilowatts?
Solution:Watts = 12,000 x 0.29307 = 3,516.85 W Kilowatts = 3,516.85 / 1000 = 3.517 kW Horsepower = 3,516.85 / 745.7 = 4.716 hp
Result:12,000 BTU/h = 3,516.85 W = 3.517 kW = 4.72 hp
Frequently Asked Questions
What is the difference between a watt and a horsepower?
A watt is the SI unit of power equal to one joule per second. One mechanical horsepower equals 745.7 watts. Horsepower was originally defined by James Watt to compare steam engine output to the work capacity of draft horses. He estimated that a horse could do 33,000 foot-pounds of work per minute. The metric horsepower (PS) is slightly different at 735.5 watts, defined as the power to lift 75 kilograms by one meter in one second.
How do I convert between kilowatts and horsepower?
To convert kilowatts to mechanical horsepower, divide by 0.7457 or multiply by 1.341. For example, a 100 kW engine equals about 134.1 horsepower. To convert horsepower to kilowatts, multiply by 0.7457. This conversion is commonly needed when comparing vehicle specifications between metric and Imperial markets. European cars often list power in kilowatts or PS (metric horsepower), while American specifications typically use mechanical horsepower.
What is a BTU per hour and when is it used?
BTU per hour (BTU/h) is a unit of power commonly used in the heating, ventilation, and air conditioning (HVAC) industry, particularly in the United States. One BTU per hour equals approximately 0.293 watts. Air conditioner capacities are often rated in BTU/h, where a typical window unit might produce 5,000 to 12,000 BTU/h of cooling power. One ton of refrigeration equals 12,000 BTU/h or about 3,517 watts. Furnaces and water heaters also commonly display their output in BTU/h.
What is the relationship between power and energy?
Power is the rate at which energy is transferred or converted, measured in watts (joules per second). Energy is the total amount of work done over time, measured in joules or kilowatt-hours. A 100-watt light bulb consumes 100 joules of energy every second. Running that bulb for one hour uses 0.1 kilowatt-hours (kWh) of energy. Understanding this relationship is essential for calculating electricity costs: your utility bill charges for energy consumed (kWh), not instantaneous power (W).
How do calories per second relate to watts?
One calorie per second equals exactly 4.184 watts. This relationship comes from the mechanical equivalent of heat, where one thermochemical calorie equals 4.184 joules. Since one watt is one joule per second, the conversion is straightforward. This unit is used in thermodynamics and heat transfer calculations. For context, the human body at rest produces about 80 watts of heat, equivalent to roughly 19 calories per second or about 69 kilocalories (food Calories) per hour.
What is the difference between mechanical horsepower and metric horsepower?
Mechanical or imperial horsepower is defined as 550 foot pounds per second, which works out to about 745.7 watts, and it is the figure used in US and UK ratings. Metric horsepower, written PS or CV, is defined as 75 kilogram force metres per second and equals about 735.5 watts, roughly 1.4 percent less. European engine outputs are often quoted in PS, so a car listed at 200 PS is nearer 197 mechanical horsepower, or about 147 kilowatts.
Why do air conditioners get rated in tons of refrigeration rather than kilowatts?
A ton of refrigeration comes from the cooling rate of melting one short ton of ice over 24 hours and is defined as 12000 BTU per hour, which is about 3517 watts. The unit stuck in HVAC sizing because equipment catalogues, duct design tables and load calculations were all built around it. Converting a nominal 3 ton unit gives 36000 BTU per hour, or roughly 10.55 kilowatts of cooling capacity.
How does electrical input power differ from mechanical output power on a motor nameplate?
A nameplate horsepower or kilowatt figure states shaft output, the useful mechanical power delivered to the load. Electrical input is larger because of copper losses, iron losses, friction and windage, and the ratio of the two is the efficiency. A motor rated 10 horsepower, about 7457 watts of output, running at 90 percent efficiency draws roughly 8286 watts electrical. Sizing supply cable and breakers from output power alone therefore understates the demand.
What is the difference between peak power and continuous power ratings?
Continuous or rated power is what a machine can sustain indefinitely without exceeding its thermal limits, while peak power is a short burst tolerated only until temperature rises, often seconds to a couple of minutes. Generators, motors, amplifiers and power supplies all publish both, and the peak figure can be double or more. Convert and compare like with like, since a peak watt rating set against a competitor continuous rating is not a fair comparison.
How do I turn a power figure into a running cost?
Multiply power in kilowatts by hours of operation to get kilowatt hours of energy, then multiply by the tariff per kilowatt hour. A 1500 watt heater is 1.5 kW, so eight hours consumes 12 kWh. If a device is rated in BTU per hour or horsepower, convert to watts first using the factors this tool applies, since energy billing everywhere is settled in kilowatt hours rather than in power units.
References
Reviewed for accuracy by Manoj Kumar, Mathematics Educator ยท Editorial policy
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