What is electrical power, in simple words?
Power is how fast a device uses electrical energy. A 100-watt bulb uses energy ten times faster than a 10-watt one. The basic rule is power = voltage × current (P = V × I).
// physics › Circuits
Electrical Power
Find electrical power from voltage and current (P = VI), or from current and resistance, or voltage and resistance.
P = V I = I²R = V²/R
A mind behind this: Georg Ohm 1789–1854
Frequently asked questions
Why are there three formulas?
Because of Ohm's Law (V = IR) you can swap things in. If you know voltage and current, use P = V×I. Know current and resistance? Use P = I²×R. Know voltage and resistance? Use P = V²÷R. All three give the same power — just pick the one matching what you know.
Can you show an example?
A device runs at 12 volts and draws 2 amps. Power = 12 × 2 = 24 watts. If instead you knew it had 6 ohms of resistance at 2 amps: P = 2² × 6 = 24 watts too. Same answer.
What is a watt?
A watt is one unit of energy (a joule) used every second. So a 60-watt bulb uses 60 joules of energy each second it is on.
Is this the same as the mechanical power calculator?
No — they are different. Mechanical power is about work and motion (P = W/t = F×v), while electrical power is about circuits (P = V×I). Same idea of 'energy per second', but different quantities, so they are separate calculators.
Why does this matter for my electricity bill?
Your bill is based on energy used, which is power × time (kilowatt-hours). A high-power appliance left on for a long time uses the most energy — which is why heaters and dryers cost more to run than a phone charger.