Electrical Power Calculator (P = V·I)
Electrical power calculator: P = V·I. Find watts from volts and amps, or the current an appliance draws.
P = V · I
How to use this calculator
- Choose the quantity you want under “Solve for”.
- Type the known values and pick their units: any combination works.
- The result updates as you type. Open “Show the steps” to see the substitution.
Electrical power is voltage times current, P = V·I. A 120 V outlet supplying 10 A delivers 1,200 W.
The calculator also gives the equivalent resistance and the energy used in one hour, in kWh, to estimate running costs.
Formula
P = V · I
| Symbol | Quantity | Units |
|---|---|---|
| V | Voltage | V, mV, µV, kV |
| I | Current | A, mA, µA, kA |
| P | Power | W, mW, kW, MW, hp, PS, BTU/h, kcal/h |
Worked example
Given: V = 230 V · I = 10 A
P = V · I
Result: P = 2 300 W
Frequently asked questions
How many amps does a 1,500 W heater draw on 120 V?
I = P/V = 1500/120 = 12.5 A.
Does this work for AC?
For resistive loads, yes, using RMS values. Motors and electronics have a power factor below 1, so real power is P = V·I·cos φ.