Watt (W)

The watt (W) is the SI unit of power and measures the rate at which energy is consumed, generated, or transferred. One watt equals one joule per second (1 W = 1 J/s). The unit is named after James Watt, a pioneer in steam engine technology.

Power Calculation in Electrical Circuits

In electrical systems, power is most commonly calculated as:

P = V × I

where:

• P = power (W)

• V = voltage (V)

• I = current (A)

Other equivalent formulas include:

• P = I² × R

• P = V² / R

where:

• R = resistance (Ω)

These formulas express power in terms of Ohm’s Law and are used depending on the known variables.

Practical Applications

• A 60 W incandescent light bulb consumes 60 joules per second, while an equivalent LED uses only 8–15 W.

• An industrial motor rated at 5 kW (5,000 W) delivers mechanical energy to operate heavy equipment efficiently.

The watt is a key unit across disciplines—from consumer electronics and electrical infrastructure to power generation and industrial control systems.