watt

Everyday

1. (science) The unit used to measure power: how fast energy is used or produced. One watt is one joule of energy every second. tree →
2. (a name) James Watt was a Scottish engineer who improved the steam engine; the unit is named after him. tree →

In the lessons

In science and energy lessons watts tell how powerful a device is: a light bulb might use 10 watts, a kettle 3,000 watts (3 kilowatts). Saving energy means choosing devices with fewer watts and switching them off. Electricity bills count kilowatt-hours. Phrases: a 60-watt bulb, kilowatt, megawatt, watts of power.

Examples

• An LED bulb uses only about 10 watts. tree →
• The kettle uses 3,000 watts, or 3 kilowatts. tree →
• A watt is a unit of power. tree →
• The watt is named after James Watt. tree →
• Which uses more watts, the hairdryer or the phone charger? tree →
• The wind turbine makes two million watts, or two megawatts. tree →

Note

Symbol W; 1 kilowatt (kW) = 1,000 watts; 1 megawatt (MW) = 1,000,000 watts. Homophone trap: watt sounds like "what". Maths: energy = power × time, so a 100-watt lamp on for 10 hours uses 1,000 watt-hours = 1 kilowatt-hour. Watts measure power, volts measure electrical push, amps measure current.