Watt (W)
The SI unit of power equal to one joule per second
The Watt (W) measures the rate of energy transfer and has a history connected to the Industrial Revolution, when engineers needed ways to compare the output of steam engines with familiar reference points. James Watt popularized the concept of horsepower to help sell his steam engines by comparison to the work a horse could do. Today the watt — named after Watt — is the SI unit of power. The Watt reflects the conventions of its origin industry, whether electrical engineering, automotive performance, or heating and cooling.
Accurate power measurement is critical in engineering, science, commerce, and everyday life. Using the correct unit and applying conversions precisely prevents errors that can be costly or dangerous in professional applications.
Conversion Table
| Unit | Symbol | 1 W = |
|---|---|---|
| Kilowatt | kW | 0.001 kW |
| Horsepower | hp | 0.00134102 hp |
| BTU per Hour | BTU/hr | 3.41214 BTU/hr |
Conversions Involving Watt
Common Uses of the Watt
- •Electrical engineering — sizing circuits, transformers, and generators
- •Automotive — comparing engine output ratings across vehicles
- •HVAC — specifying heating and cooling equipment capacity
- •Industrial machinery — selecting motors and drives for process equipment
- •Renewable energy — rating solar panels and wind turbine output
Did You Know?
The International Bureau of Weights and Measures (BIPM) in Sèvres, France, is the custodian of the International System of Units (SI). The BIPM coordinates global measurement science and maintains the definitions of base units that underpin all scientific and industrial measurement. The Watt is part of this global measurement framework that ensures a scientific result in one country means exactly the same thing when replicated in another. This traceability is essential in fields from pharmaceutical manufacturing to aerospace engineering where measurement errors can have serious consequences.