Why is energy used by household appliances billed in kilowatt-hours rather than joules?

• A. kWh is a convenient larger unit for ongoing energy; 1 kWh = 3.6 × 10^6 J (3.6 MJ).
• B. kWh is smaller and more precise than joules.
• C. kWh is used because it is easier to convert to watts.
• D. kWh is equal to joules divided by 1000.

Answer: (A)

Energy used in households is tied to both how strong an appliance is and how long it runs. That’s why the billing unit is kilowatt-hours: it directly measures energy over time. A kilowatt-hour is the amount of energy consumed when a device rated at 1 kilowatt runs for 1 hour. Since 1 kilowatt-hour equals 3.6 × 10^6 joules, this scale makes the numbers manageable for typical monthly usage. It also aligns with pricing, which is set per kilowatt-hour of energy used. The other ideas aren’t correct because kilowatt-hours aren’t smaller than joules, they’re larger; it isn’t a unit of power, so it isn’t a direct conversion to watts; and the precise relation isn’t joules divided by 1000.