Power Converter

Power Converter handles watts, kilowatts, horsepower and the heating and cooling units. Power is energy per unit time, which is why it has its own set of units: a kilowatt hour is energy, a kilowatt is the rate at which it is used.

There are two horsepowers and they differ by about one and a half per cent. Mechanical horsepower is 745.7 watts, used in Britain and America; metric horsepower, or PS, is 735.5 watts and is what German and Japanese car specifications quote. A 150 PS car is about 148 hp, which is why the same engine is advertised with two different figures in two markets.

BTU per hour is the air conditioning and heating unit, and the conversion is worth knowing: 12,000 BTU/h is one ton of refrigeration, which is about 3.52 kilowatts. That is where the 9,000, 12,000 and 18,000 BTU air conditioner sizes come from.

The page shows its working, not just its answer. Where there is a formula it is printed with your own numbers substituted in, so you can check the result rather than take it on trust -- which is the difference between a calculator you can use for something that matters and one you cannot.

Everything runs inside your browser. What you type is never uploaded, never logged and never stored, and the calculator keeps working if your connection drops after the page has loaded.

• Shows result, to twelve digits, conversion factor, the other way and in scientific notation together, so you are not running it twice
• A results table you can read across
• Updates as you type, with no button to press and no page reload
• Copy the result in one click
• Free, no sign-up, and it runs entirely in your browser

The power converter is used by writers, developers, students, marketers and anyone else who needs the job done once without installing software. Common cases include:

• Converting a car engine from horsepower to kilowatts
• Comparing a PS figure with an hp figure
• Converting an air conditioner rating from BTU/h to kW
• Getting the power of a heater in watts