How is Wattage Calculated?

••• Chuck Coker, Pembroke Dave, Ian Bailey-Mortimer, Rennett Stowe, and Jim Barton at


Wattage is Analogous to the Power of Water From a Hose

The unit of measurement for electrical power is the watt. Wattage represents the amount of work done or electricity consumed per unit time. One watt is defined as one joule per second. Wattage is the product of voltage and current.

Wattage can be thought of like the power of water coming from a hose. The power of the water is a product of pressure and flow rate.


Voltage Is Similar to Water Pressure

Voltage represents the electric potential of energy. It can be thought of similar to water pressure within a hose.

One volt is defined as one joule per coulomb. A joule is the work done by one ampere of current passing through one Ohm of resistance for one second. A coulomb is one unit of electrical charge.


Current is the Flow Rate of Electrical Charge

Current represents the flow of electrical charge per unit time. It can be likened to the flow rate of water through a hose. The ampere or amp is the unit used for expressing current. One ampere equals one coulomb per second.

Calculating Wattage

Wattage Represents the Energy Consumption of an Appliance Per Unit Time

The formula for calculating wattage is:

W (joules per second) = V (joules per coulomb) x A (coulombs per second) where W is watts, V is volts, and A is amperes of current.

In practical terms, wattage is the power produced or used per second. For example, a 60-watt light bulb uses 60 joules per second. The wattage of the light bulb is the product of the voltage at which it operates and the rate of the current flowing through it.


About the Author

Carla Boulianne is an evolutionary biologist by training and freelance writer by passion. In addition to writing for Demand Studios and eHow, she is feature writer for Parenting a Gifted Child at She thrills in exploring new topics through extensive research.

Photo Credits

  • Chuck Coker, Pembroke Dave, Ian Bailey-Mortimer, Rennett Stowe, and Jim Barton at