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 = 1 kg·m²/s³). 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 follow from Ohm’s law for DC circuits and resistive loads. For alternating-current systems, real power also depends on phase relationship or power factor.

Practical Applications

• A device operating at 60 W transfers or converts 60 joules of energy per second.

• A power rating of 5 kW corresponds to an energy-transfer rate of 5,000 joules per second.

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