Kilowatt-hour (kWh)

Definition

One kilowatt for one hour, exactly 3.6 megajoules — the electricity billing unit.

History

The kilowatt-hour is the energy of one kilowatt sustained for one hour, exactly 3.6 megajoules. It became the standard way to bill electricity as power grids spread.

Where it is used

Kilowatt-hours are the unit on electricity bills and describe the capacity of batteries, including electric-vehicle packs.

Typical uses include electricity bills, EV batteries.

Conversion pages

These pages convert kilowatt-hour to or from another unit in energy.

• Kilowatt-hour to joule
• British thermal unit to kilowatt-hour

Other Energy units

• Kilocalorie (kcal)
• Kilojoule (kJ)
• Calorie (cal)
• Joule (J)
• British thermal unit (BTU)
• Watt-hour (Wh)

Sources

• NIST SP 811 NIST SP 811, Appendix B; ISO 80000-5 (energy) · Dataset reviewed Nov 11, 2026