Energy Converter

Convert between joules, kilojoules, calories, kilocalories, watt-hours, kilowatt-hours, BTU, and foot-pounds.

About this Calculator

Convert between joules, kilojoules, calories, kilocalories, watt-hours, kilowatt-hours, BTU, and foot-pounds.

Formula & Calculations

Formula

Result = Input value × (Conversion factor from unit / Conversion factor to unit), normalized to joules

Where:

J=Joules (SI base unit of energy)
kJ=Kilojoules (1 kJ = 1000 J)
cal=Calories (1 cal = 4.184 J)
kcal=Kilocalories / food Calories (1 kcal = 4184 J)
Wh=Watt-hours (1 Wh = 3600 J)
kWh=Kilowatt-hours (1 kWh = 3,600,000 J)
BTU=British Thermal Units (1 BTU = 1055.06 J)
ft·lb=Foot-pounds (1 ft·lb = 1.35582 J)

Assumptions

All conversions use the joule as the intermediate base unit.
Calorie values use the thermochemical calorie (1 cal = 4.184 J).
BTU uses the ISO definition (1 BTU = 1055.06 J).

Calculation Examples

Example 1

Inputs:1000 Joules to kilocalories

Result:0.239 kcal

1000 ÷ 4184 = 0.239 kcal.

Example 2

Inputs:1 kWh to Joules

Result:3,600,000 J

1 × 3,600,000 = 3,600,000 J.

Example 3

Inputs:500 calories to Joules

Result:2092 J

500 × 4.184 = 2092 J.

Frequently Asked Questions

What is the difference between calories and kilocalories?

A kilocalorie (kcal) is 1000 calories. Food labels typically show 'Calories' with a capital C, which actually means kilocalories. This calculator treats cal as small calories and kcal as large/food Calories.

What is a BTU and where is it used?

A British Thermal Unit is the energy needed to raise 1 pound of water by 1°F. It is commonly used in heating and air conditioning equipment ratings, especially in the United States.