Electrical Power (P = VI)

Also known as P = VI · watts law · power from volts and amps

P = V I

P =

V =

I =

Enter your known values, leave one input blank, and solves for the missing one. Try different units for next level excitement!

Learning zone

This formula falls straight out of the definitions. A volt is a joule per coulomb — the energy each unit of charge carries — and an ampere is a coulomb per second — how many units of charge arrive each second. Multiply them and the coulombs cancel, leaving joules per second: watts. A 1500 W space heater on a 120 V household circuit draws 1500/120 = 12.5 A, which is why it crowds a standard 15 A breaker and shouldn't share the circuit with much else.

Unlike the resistor-specific forms P = I²R and P = V²/R, this version works for any component — ohmic or not — including motors, LEDs, and batteries, because it comes from the definitions of voltage and current rather than from Ohm's law. Electric utilities meter exactly this product, accumulated over time, when they bill you for energy.

Electrical Power (P = VI)

P = V I

Where

$P$ = Power
$V$ = Voltage
$I$ = Current

Missing one of these? Work it out first, then come back

Power — Electrical Power (P = I²R), Electrical Power (P = V²/R)
Voltage — Ohm's Law, Electrical Power (P = V²/R)
Current — Ohm's Law, Electrical Power (P = I²R)

Part of this formula set

The Ohm's law wheel

4 formulasOhm's law and the three power equations, arranged so that each one omits exactly one of voltage, current, resistance and power.