Convert BTU to Watt-hours

About converting BTU to Watt-hours

BTU (BTU) and Watt-hours (Wh) are both units of energy, so converting between them is a single multiplication: multiply your BTU figure by 0.2931. Ten BTU comes to 2.9307 Watt-hours, and a hundred works out at 29.3071 Watt-hours.

Rule of thumb: going from BTU to Watt-hours divides, so the figure always shrinks — it takes about 3.4121 BTU to make a single Watt-hour. If your answer came out bigger, you have the conversion the wrong way round.

What is a BTU?

The BTU is the heat needed to raise one pound of water by one degree Fahrenheit — and there is no single BTU. Water takes slightly different amounts of heat to warm depending on the temperature it starts from, so several definitions exist (thermochemical, International Table, 39 °F, 59 °F, 60 °F and others), differing from one another by a fraction of a percent. This converter uses one common value, so treat the result as convention-dependent rather than absolute. In the US it is the unit of heating and cooling capacity, though air conditioners are really rated in BTU per hour and the "per hour" is routinely dropped in marketing.

What is a Watt-hour?

A watt-hour is energy, not power, and that distinction trips people up constantly. A watt is a rate — energy per second — so a watt-hour is what you get by sustaining that rate for an hour: a quantity of energy expressed as "this much power for this long". It is the natural unit for anything that stores energy and releases it gradually, which is why phone and laptop batteries are rated in watt-hours rather than the milliamp-hours stamped on the cell, and why airlines police lithium batteries by their watt-hour rating. Capacity in watt-hours tells you how long a load can run; watts alone never can.

To put both in perspective: a wooden kitchen match releases roughly one BTU, while a phone battery holds somewhere around 15 watt-hours.

The converter above updates as you type, and the table lists common values for quick reference. Need the opposite direction? Use the Watt-hours to BTU converter, or browse all Energy converters.