Convert Watt-hours to BTU

About converting Watt-hours to BTU

Watt-hours (Wh) and BTU (BTU) are both units of energy, so converting between them is a single multiplication: multiply your Watt-hours figure by 3.4121. Ten Watt-hours comes to 34.1214 BTU, and a hundred works out at 341.2142 BTU.

Rule of thumb: going from Watt-hours to BTU multiplies, so the figure always grows — one Watt-hour is already 3.4121 BTU. If your answer came out smaller, you have the conversion the wrong way round.

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.

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.

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

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