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Energy Units Explained
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The Joule (J) is the SI unit of energy. A kilowatt-hour (kWh) is the energy used by a 1,000-watt appliance in one hour — it's what your electricity bill measures. A food Calorie (capital C) is actually a kilocalorie (1,000 small calories). One BTU (British Thermal Unit) is the energy needed to heat one pound of water by 1°F.
A kilowatt-hour (kWh) is the amount of energy used by a device running at 1,000 watts (1 kilowatt) for one hour. It equals 3,600,000 Joules (3.6 MJ). Electricity bills are measured in kWh — in the US, the average household uses about 877 kWh per month. A 100W light bulb uses 0.1 kWh per hour, costing about 1–2 cents.
A food "Calorie" (capital C) is actually a kilocalorie — 1,000 chemistry calories. When a food label says 200 Calories, it means 200 kcal or 200,000 small calories or 836,800 Joules. The chemistry calorie is the energy to heat 1 gram of water by 1°C. Always check whether "calorie" or "Calorie" is used when converting.