Energy is work done. It is power × time.
Electrical energy is power (most commonly stated in watts) times a unit of time (most commonly 1 hour: watt-hours). 1,000 watt-hours equals one kilowatt-hour (kWh), which is the amount of power in watts transferred (or used) over 1 hour divided by 1,000. A MWh is equal to 1,000 kWh or 1,000,000 watt-hours. All other metric prefixes can also be applied, e.g., giga (G, billion), tera (T, trillion), and peta (P, quadrillion).
For comparison or inclusion with other forms of energy, electrical energy can also be measured in joules (J), British thermal units (BTUs), and million tonne oil equivalent (mtoe). One petajoule (PJ) = 278 GWh. One quadrillion BTU (quad) = 293 TWh. One mtoe = 11,630 GWh.
The total amount of electricity (including commercial and industrial use as well as residential) used in the USA in 2016 was 3.85 PWh (3.85 trillion kWh). With a population of around 323 million, the per-capita (per-person) electricity consumption in the USA was therefore about 12,000 kWh (12 MWh) in 2016.
- The spelling tonne is used to specify a metric ton, which is equal to 1,000 kilograms (kg), or 2,205 pounds. A non-metric ton is equal to 2,000 pounds in the USA (also called a short ton), and 2,240 pounds in the UK (also called a long or imperial ton, equal to 160 [20 × 8] stone).