Energy Converter
Convert joules, calories, kilowatt-hours, and BTU.
Conversion sheet
DIY at your own risk. Calcora's calculators and guides are general estimates and information only — not professional, engineering, legal, or safety advice. Always verify local building codes and permit requirements, and hire a licensed pro for electrical, gas, plumbing, structural, or any work you're not fully comfortable doing yourself.
Energy appears on nutrition labels as calories, on electric bills as kilowatt-hours, and in heating specs as BTU. They all measure the same quantity, and this converter pivots every one through the joule, the SI base unit.
How it works
Energy values convert through joules as the base unit.
The joule is the base. A 'calorie' here is the scientific small calorie (4.184 J); the food Calorie you see on a label is actually a kilocalorie, 1000 of these, which is why diet figures use the kilocalorie row.
Kilowatt-hours connect energy to power and time: 1 kWh is 3,600,000 joules, the energy a 1000-watt appliance uses in one hour. BTU (1055.06 J) is common in US heating and cooling equipment.
Result = (value × joules-per-source-unit) ÷ joules-per-target-unit.
Worked examples
Convert 1 kilowatt-hour to joules. → 3,600,000 joules
1 kWh = 3600 × 1000 J = 3,600,000 J.
Convert 1 kilowatt-hour to kilocalories. → 860.42 kilocalories
3,600,000 J ÷ 4184 J per kcal = 860.42 kcal.
Tips & gotchas
- Food 'Calories' (capital C) are kilocalories. A 500-Calorie meal is 500 kcal, which is about 2.09 million joules — use the Kilocalories row.
- To estimate an appliance's running cost, find its kilowatt-hours (watts × hours ÷ 1000) and multiply by your electricity rate.
- BTU is the unit on furnace and air-conditioner labels in the US. One BTU is about 1055 joules, so a 10,000 BTU unit delivers about 10.55 megajoules per hour.
- Watt-hours (3600 J) are handy for batteries and power banks; a 10,000 mAh, 3.7 V bank stores about 37 Wh.
FAQ
Is a food Calorie the same as the calorie in this tool?
No. A food Calorie is a kilocalorie (1000 small calories). Use the Kilocalories row for nutrition figures, not the Calories row.
How many joules are in a kilowatt-hour?
Exactly 3,600,000. A kilowatt-hour is 1000 watts running for 3600 seconds, and a watt is one joule per second.
What is a BTU and where is it used?
A British Thermal Unit (about 1055 joules) is the energy to heat one pound of water by 1°F. It's standard on US heating and air-conditioning equipment.
Related calculators
Length Converter · Weight Converter · Temperature Converter · Volume Converter · Speed Converter