Convert Calories to BTU

About converting Calories to BTU

Calories (cal) and BTU (BTU) are both units of energy, so converting between them is a single multiplication: multiply your Calories figure by 0.003966. Ten Calories comes to 0.03966 BTU, and a hundred works out at 0.3966 BTU.

Rule of thumb: going from Calories to BTU divides, so the figure always shrinks — it takes about 252.1644 Calories to make a single BTU. If your answer came out bigger, you have the conversion the wrong way round.

What is a Calory?

The calorie is the unit most likely to be misread, because there are two of them. The small calorie — the one this converter uses — is approximately the heat needed to warm a gram of water by one degree Celsius, and it is a tiny amount of energy. The "calories" printed on food labels are not these: a food Calorie, traditionally written with a capital C, is a thousand small calories, properly a kilocalorie. So a 2,000-calorie daily diet is really about 8.4 million small calories. Several slightly different calories were defined historically; the thermochemical calorie used here is fixed at exactly 4.184 joules.

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: an apple holds roughly 95,000 small calories, 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 Calories converter, or browse all Energy converters.