Energy Converter (kJ, kcal, kWh, BTU)
Kilojoules to calories, kilowatt-hours to joules, food labels, electricity bills and heating specs on one scale.
Free forever, no sign-up and no limits, and this tool installs on its own so you can keep it on your home screen.
Kilojoules to kilocalories, kilowatt-hours to joules, BTU to kWh, food labels, electricity bills and heating specs finally on one scale, converted exactly as you type.
How to use it
- Pick the unitskcal and kJ are preloaded, the food-label pair. Watt-hours and BTU cover bills and heating.
- Type the valueThe answer appears as you type; Swap flips the direction.
- Check the factorThe exact multiplier is printed under the answer.
One quantity, four bills
Energy is the quantity you pay for most often under the most disguises: kilocalories on food, kilowatt-hours on electricity, BTU on the air conditioner box, megajoules on gas in some countries. They are the same physical stuff (a joule is a joule) but the units grew up in different industries and never reconciled. The practical consequence is that comparing anything across those worlds needs a converter, and the comparisons are where the insight lives.
Numbers that put watts in perspective
A resting human runs on about 100 W: 2,000 kcal spread over a day. A phone charge is around 0.015 kWh, which at typical tariffs costs less than half a cent; the same energy is in about 13 kcal of food, a single bite of a sandwich. Heating water dominates domestic energy: one hot shower (~1.5 kWh) equals a hundred phone charges. Running these through the converter turns abstract efficiency advice into arithmetic you can check, which uses more energy stops being a matter of opinion.
Questions people ask
How do I convert kJ to calories on a food label?
Divide by 4.184, a label's 2,000 kJ is 478 kcal. The mental shortcut is divide by 4 and take a bit off. What food packaging calls a calorie is really a kilocalorie; the lowercase calorie is a thousand times smaller and only appears in chemistry.
What is a kilowatt-hour, physically?
The energy of running a 1,000-watt appliance for an hour, exactly 3.6 million joules. It is the unit on your electricity bill: a heater at 2 kW for 3 hours costs 6 kWh times your tariff. Kettle to boil: about 0.1 kWh.
How do food and electricity compare?
A day's food, 2,000 kcal, is about 2.3 kWh, roughly the electricity of one dishwasher cycle. The comparison runs through this converter and never fails to surprise: bodies run on remarkably little power, about 100 watts.
What is a BTU and why is it on my air conditioner?
The energy to heat a pound of water by one degree Fahrenheit: 1,055 joules. US heating and cooling equipment is rated in BTU per hour: a 12,000 BTU/h air conditioner moves about 3.5 kW of heat. Divide BTU/h by 3,412 for kilowatts.
Which calorie does this tool use?
The thermochemical calorie, defined as exactly 4.184 joules, with the food kilocalorie exactly a thousand of those. Older texts sometimes used a 4.1868 J calorie; the difference is 0.07% and matters to nobody's diet.
How many joules are in a kilowatt-hour?
Exactly 3,600,000, or 3.6 megajoules. A kilowatt drawn for one hour is a thousand joules a second for 3,600 seconds, so the figure is a definition rather than a measurement. It is the conversion that turns an electricity bill into physics.