🔌 Power

Power Converter

Car engines in horsepower, heaters in kilowatts, air conditioners in tons of refrigeration — convert every rate of energy transfer. Press Convert.

Written and reviewed by SM Arijul Islam · Last reviewed · Editorial standards · Report an error

About the power converter

Power is energy per unit time, measured in watts (one joule per second). Two different horsepower standards are still in use: mechanical/imperial horsepower (745.7 W) and metric horsepower, or PS (735.5 W). This converter includes both so you always know which one you have.

Factors used

  • 1 kW = 1,000 W · 1 MW = 1,000,000 W
  • 1 mechanical horsepower = 745.6998715823 W
  • 1 metric horsepower (PS/PK) = 735.49875 W
  • 1 BTU/h = 0.29307107017222 W
  • 1 ton of refrigeration = 3,516.8528420667 W
Electricity cost = power (kW) × hours × price per kWh — see the Finance Calculator for compound growth.

How to convert power

Power is the rate at which energy is used or produced, measured in watts (W). One watt is one joule per second. A kilowatt is a thousand watts and a megawatt a million. Mechanical power is also quoted in horsepower, and the definitions differ: one mechanical horsepower is about 745.7 W, while the metric horsepower used across much of Europe is about 735.5 W — a difference worth roughly 1.4%.

Common power conversions

One kilowatt expressed in other units of power
Unit1 kilowatt equals
Microwatt (µW)1,000,000,000
Watt (W)1,000
Horsepower (metric, PS) (PS)1.3596216
Horsepower (mechanical) (hp)1.3410221
Megawatt (MW)0.001
Gigawatt (GW)0.000001

Everyday uses

  • Comparing appliance running costs
  • Engine, motor and generator ratings
  • Sizing solar panels and inverters
  • Heating and air-conditioning output
  • Planning electrical circuits and loads

Frequently asked questions

About 745.7 W for mechanical horsepower, or about 735.5 W for metric horsepower.
Watts measure the rate of energy use, while watt-hours measure total energy: 1,000 W for one hour is 1 kWh.
Mechanical, metric, electrical and boiler horsepower are separate definitions, so always check which one a datasheet uses.
Multiply the power in kilowatts by the hours used and by your price per kilowatt-hour.

More worked examples

  • One mechanical horsepower is 745.7 watts.
  • A 2,000 W heater draws about 8.7 amps on a 230 V supply.
  • One kilowatt is about 1.341 mechanical horsepower.
  • A 3,000 W appliance on a 120 V circuit draws 25 amps.

Quick reference

Common power units expressed in watts
UnitIn watts
1 watt1 joule per second
1 kilowatt1,000 W
1 megawatt1,000,000 W
1 mechanical horsepower745.6999 W
1 metric horsepower (PS)735.49875 W
1 BTU per hour0.293071 W
1 ton of refrigeration3,516.85 W

Common mistakes to avoid

  • Assuming all horsepower values are equal. Mechanical is 745.7 W, metric is 735.5 W, electrical is 746 W and boiler horsepower is about 9,810 W.
  • Confusing kilowatts with kilowatt-hours. Power is a rate, energy is that rate sustained over time.
  • Using watts equals volts times amps for alternating current without the power factor, which overstates the real power.
  • Comparing a motor's rated output with its input draw, which is higher because of losses.

Further questions

One joule per second, the SI unit of power named after James Watt.
About 745.7 W for mechanical horsepower, the figure used for engines in most countries. Metric horsepower is 735.5 W.
Because current and voltage can be out of phase, so the useful power is V × A × power factor, which is always at or below the apparent power.
Apparent power, the simple product of volts and amps. Transformers and uninterruptible power supplies are rated this way.

Sources and standards

Power is energy per unit time, so the watt is one joule per second. NIST SP 811 supplies the mechanical and electrical horsepower factors, and the boiler and metric horsepower figures are labelled separately because they differ.

Related converters

Energy Converter Voltage Converter Electric Current Converter Resistance Converter