What is a Watt?

The watt is the SI unit of power, equal to one joule per second (1 W = 1 J/s). Named after Scottish engineer James Watt (1736–1819), whose improvements to the steam engine sparked the Industrial Revolution, the watt unifies mechanical, electrical, and thermal power. A typical LED bulb consumes 8–12 W to produce as much light as a 60-W incandescent bulb. Human resting metabolism is about 80–100 W of heat output, while peak athletic performance reaches 400–1,500 W (briefly). The watt is fundamental in electrical engineering: P = V × I (power = voltage × current). It relates to the kilowatt (1 kW = 1,000 W), the megawatt (1 MW = 10⁶ W), horsepower (1 hp ≈ 745.7 W), and the BTU per hour (1 W ≈ 3.412 BTU/h). Light bulb and appliance ratings, electric motor outputs, and audio amplifier specifications all use the watt as the base unit.

Visual reference for how the watt relates to other power units. Each row links to the full converter for that pair.

• Light-bulb and appliance ratings
• Scientific and engineering power specs
• Radio and electronics power

• ✓1 W = 1 J/s = 1 V × 1 A (for DC).
• ✓LED lighting: 10× more efficient than incandescent.
• ✓For home appliances, rating × hours used = kWh.

• ✗Confusing watts (power) with joules (energy).
• ✗Assuming "100 W bulb" for LED — old incandescent rating.
• ✗Mixing W with V or A — different quantities.