Power and energy
Electrical power: VI
- where
- power (W)
- voltage (V)
- current (A)
Explain this equation
Works out power from voltage and current. Used to size loads and estimate current draw for DC circuits and resistive AC loads.
P is the rate at which energy is delivered, in watts. V is the voltage across the load and I is the current through it.
Voltage is energy per coulomb and current is coulombs per second, so multiplying them gives energy per second, which is watts.
Sense check: 230 V at 10 A is 2,300 W. A 13 A load on 230 V is about 3 kW.
Watch out: on AC with motors, transformers or electronic loads, V × I gives volt-amperes. Real power needs the power factor as well.
Power is the rate of energy transfer. For a steady DC load, multiplying its voltage by current gives watts.
Rearrange to I = P/V when estimating a DC load current. General AC real power also needs power factor, covered later.
Enter your values to see the result.
Common mistake
Using VI as real AC watts when power factor is below one.
Limits
Steady DC or unity-power-factor AC using RMS values.
Sources
The tools calculate the displayed equation. They do not automatically choose cable sizes, approve installations, supply current regulatory tables, certify equipment or replace inspection and testing.