How to convert heat and energy units

The Heat and Energy Converter changes a value between eight units of heat and energy: calorie, kilocalorie, kilowatt-hour, horsepower-hour, metric horsepower-hour, kilogram-force metre, British thermal unit and foot-pound force. Type a number in the row that matches the unit you have, press Convert in that row, and the other seven rows fill with the equivalent amounts.

The conversion runs in this browser from fixed definitions, so the page keeps working offline and nothing you type is uploaded. Results are rounded to twelve significant digits, and a value that cannot be read leaves the other rows empty instead of showing stale numbers.

Type the value in the row of its unit, for example 1 in the Kilocalorie row. Decimals use a point — write 1.5, not 1,5 — and thousands separators such as 1,000 are not accepted.
Press Convert in that row, or press Enter inside the field. The other seven rows are replaced with the equivalents, while the row you typed in keeps the text exactly as entered.
Read the row you need: 1 kcal shows 1000 cal, 0.00116222222222 kWh and 3.96566683139 BTU, and 1 kWh shows 860.420650096 kcal.
Press Reset all to empty the eight fields and clear the status line, or simply type over a result you no longer need.

Definitions, rounding and limits

The eight units and their definitions

Every row converts through the joule, so each unit is one fixed number: 1 calorie = 4.184 J, the thermochemical calorie behind the 4184 J food calorie; 1 kilocalorie = 1000 cal = 4184 J; 1 kilowatt-hour = 3.6 MJ; 1 kilogram-force metre = 9.80665 J; 1 BTU = 1055.05585262 J, the International Table definition; and 1 foot-pound force = 0.3048 m × 0.45359237 kg × 9.80665 m/s² = 1.3558179483314 J.

The two horsepower-hours are different units and are easy to confuse. The metric horsepower-hour (PS·h) is 75 kgf·m/s × 3600 s = 2.6477955 MJ, the mechanical horsepower-hour (hp·h) is 550 ft·lbf/s × 3600 s = 2.684519537696 MJ, about 1.4 % more. A figure copied from a European rating and one from an American rating therefore do not match exactly, and 1 hp·h reads 1.01386966542 PS·h here.

Rounding, input and the status line

Results carry twelve significant digits. Amounts between 1e-6 and 1e12 are written as plain decimals and anything outside that window as exponent notation, so 0.000001 cal reads 4.2664926351e-7 kgf·m rather than a long row of binary noise, and 1 Btu reads 252.164400722 cal.

A comma is refused with an explanation instead of being deleted, because half the languages this page is served in use it as the decimal mark and the legacy filter turned 1,5 into 15 without a word. Exponent notation such as 1e3 is accepted, a negative value keeps its sign, and the status line under the table names the row that was converted.

What this converter does not do

It converts units of energy only. The heat equation Q = c·m·Δt, which needs a specific heat capacity and a temperature difference, is not part of this page, and nor is a food database: a calorie here is a unit, not a portion. Mass, volume, power and temperature have their own converters on this site.

The rows are units of energy, not of energy per second, so a watt figure belongs in the power converter. Nothing here validates a physical measurement either: the arithmetic is exact for the definitions above, but the measurement it came from is only as good as its source, so check the unit before the number whenever the result feeds a report.