๐ฅ Energy Converter
Convert between joules (J), calories (cal), watt-hours (Wh), BTU, and other energy units in real time. Handy for comparing food calorie labels with electricity usage, science homework, or checking the specs of imported appliances.
How to use
- Enter a value into any energy unit field (J, kJ, cal, kcal, Wh, kWh, or BTU).
- The converted values appear instantly in the other unit fields.
How the calculation works
The SI unit of energy is the joule (J), the work done by a one-newton force moving an object one metre. The calorie was originally the heat needed to raise one gram of water by one degree Celsius; today it is converted as 1 cal = 4.184 J (the thermochemical calorie). The "kcal" on food labels is a thousand of those. A watt-hour (Wh) is one watt used for an hour: 1 Wh = 1 W ร 3,600 s = 3,600 J. The kWh on an electricity bill is a thousand times that, 3,600,000 J (3.6 MJ). The British Thermal Unit (BTU), about 1,055 J, appears mainly on American heating and cooling equipment. The units come from very different places, but they all measure the same thing, so going through joules lets you compare the energy in food with the energy on your electricity bill.
Worked example
The energy in a 180 kcal rice ball kJ: 180 ร 4.184 โ 753 kJ Wh: 180 ร 4,184 รท 3,600 โ 209 Wh That is about 0.21 kWh โ enough to run a 100 W device for around two hours. Conversely, 1 kWh is 3,600,000 รท 4,184 โ 860 kcal.
Things to be aware of
- There are several calorie definitions, including the thermochemical (4.184 J) and International Steam Table (4.1868 J) calories. This tool uses 4.184 J.
- Food "calories" are usually kcal; in English a capitalised "Calorie" often means kcal too.
- The energy the body extracts from food is not the same as its heat of combustion; nutrition labels account for digestion.
- BTU definitions vary slightly. This tool uses about 1,055.06 J.
FAQ
What's the relationship between calories and joules?
1 cal is about 4.184 J. This is useful for comparing nutrition labels in kcal with electricity usage in kWh or J.
Can I use this to estimate my electricity bill?
It's useful for converting kWh to other units, but for an actual bill estimate, try our Electricity Bill Calculator.
What is a BTU?
BTU stands for British Thermal Unit, commonly used to rate the capacity of air conditioners and heaters, especially in US-made products.