Power Converter
Convert between watts, kilowatts, megawatts, mechanical horsepower, metric horsepower, BTU/hour, calories/second, foot-pounds/minute, and more.
All Unit ConvertersAll conversions from 1 watt
| Unit | Symbol | Value |
|---|
How this power converter handles sixteen units, including three different horsepower definitions that are not interchangeable
Power sounds like a single concept until you notice how many industries invented their own unit for it. Electrical engineers think in watts, mechanical engineers think in horsepower, HVAC technicians think in BTUs per hour, and refrigeration techs think in tons. This tool routes every one of those through a single common unit, the watt, so any pair can be converted without a chain of intermediate lookups.
The conversion runs entirely in your browser, in plain JavaScript, with a fixed table of multipliers. Nothing you type is transmitted anywhere.
The watt as the hub unit
The watt is the SI derived unit of power, defined by the BIPM as one joule per second. Every unit in this tool carries a factor stating how many watts it equals, so converting between any two units is two multiplications instead of sixteen times sixteen separate formulas.
Three horsepower figures, three different histories
Mechanical horsepower traces back to James Watt, who defined it empirically from observations of how much work a draft horse could sustain, later standardized at 550 foot pounds per second, equal to 745.69987 watts. Metric horsepower, labeled PS for Pferdestärke, uses a slightly different reference of 75 kilogram force metres per second, working out to 735.49875 watts, a bit smaller than the mechanical figure. Electrical horsepower is a rounder, simpler value, exactly 746 watts, used mostly to rate electric motors in the United States. The tool keeps all three as distinct entries rather than collapsing them into one, because a 10 horsepower motor rating means a measurably different wattage depending on which convention the manufacturer used.
| Unit | Symbol | Watts per unit |
|---|---|---|
| Watt | W | 1 |
| Kilowatt | kW | 1,000 |
| Megawatt | MW | 1,000,000 |
| Gigawatt | GW | 1,000,000,000 |
| Milliwatt | mW | 0.001 |
| Horsepower (mechanical) | hp | 745.69987 |
| Horsepower (metric/PS) | PS | 735.49875 |
| Horsepower (electrical) | hp(E) | 746 |
| BTU per hour | BTU/hr | 0.29307107 |
| BTU per minute | BTU/min | 17.584264 |
| BTU per second | BTU/s | 1,055.05585 |
| Calorie per second | cal/s | 4.184 |
| Kilocalorie per hour | kcal/hr | 1.163 |
| Foot-pound per minute | ft·lbf/min | 0.022596966 |
| Foot-pound per second | ft·lbf/s | 1.35581795 |
| Ton of refrigeration | TR | 3,516.8528 |
What the auxiliary controls do
Swap button
Flips the from and to unit selections and reruns the conversion immediately, useful for checking a result in both directions.
Quick presets
One click preset buttons load a common value and unit pair, like 1 horsepower to watts, so you do not need to type common conversions from scratch.
Power unit references
- BIPM SI Brochure defines the watt as the coherent SI derived unit of power, equal to one joule per second.
- NIST SI derived units reference lists the watt alongside its relationship to base SI units.
- ASHRAE publishes the standardized definitions used for BTU per hour and tons of refrigeration in HVAC engineering practice.
Power ratings across industries
Comparing an engine’s horsepower rating against a generator’s kilowatt output, sizing an air conditioner from a manufacturer’s BTU per hour spec into tons of refrigeration, converting a motor nameplate figure between metric PS and imperial horsepower for an imported vehicle, and translating a solar panel’s watt rating into a more familiar unit when comparing equipment across regions.
From the blog
Reading around units
Where measurement systems came from and why two of them still argue.
