How much energy is that, really?
Energy is quoted in a dozen units — joules, calories, kilowatt-hours, BTU, tons of TNT — which is most of why nobody has a feel for it.
43% of a day of eating
1 kWh is more than 4 of the 11 references on this page.
Reference figures are measurements and are rounded; the unit conversion behind them is exact.
| Reference | Size | Yours ÷ theirs | Note |
|---|---|---|---|
| AA battery | 0.00278 kWh | 360× | |
| phone charge | 0.0139 kWh | 72× | |
| apple | 0.11 kWh | 9.07× | |
| boiling a kettle | 0.158 kWh | 6.33× | |
| day of eating | 2.33 kWh | 0.43× | A 2 000 kcal day |
| litre of petrol | 9.44 kWh | 0.106× | |
| electric car battery | 75 kWh | 1/75 | A 75 kWh pack |
| lightning bolt | 1,389 kWh | 1/1,389 | |
| home for a year | 10,694 kWh | 1/10,694 | US average electricity use |
| Hiroshima bomb | 17,500,000 kWh | 1/17,500,000 | 15 kilotons of TNT |
| the Sun in one second | 1.07×10²⁰ kWh | 1/1.07×10²⁰ |
Worth knowing
- A litre of petrol holds 34 MJ — as much energy as a person eats in four days, released in a few minutes.
- The Sun radiates more energy every second than humanity has used in its entire history, by a factor of about ten thousand.
Frequently asked
How many joules in a calorie?
4.184 exactly, by definition of the thermochemical calorie. The food "Calorie" is a kilocalorie, so 4 184 joules.
What is a kilowatt-hour?
One kilowatt sustained for one hour — 3.6 million joules. It is the unit electricity is billed in because it maps neatly onto how appliances are rated.