Electrical Power Calculator — P, V, I, R Solver
The four electrical quantities — power (P), voltage (V), current (I) and resistance (R) — are linked by P = VI, V = IR and P = I²R = V²/R. Enter any two and the other two are solved for you automatically.
W
V
A
Ω
Rate at which electrical energy is converted — P = V × I = I² × R = V² / R
- 1
Voltage × Current
12 V × 2 A = 24
How does this calculator work?
P = V × I = I² × R = V² / R — fill in any two of power (W), voltage (V), current (A) or resistance (Ω) and get the other two. The energy per hour is P/1000 kWh. Applies to DC and RMS quantities in purely resistive AC circuits. Reactive (inductive/capacitive) AC loads need a power-factor correction: P = V·I·cos φ.
Formula
How this is calculated
Electrical power is the rate at which a circuit element converts electrical energy into another form — heat in a resistor, light in an LED, mechanical work in a motor. The defining relation P = V × I links power (watts) to voltage (volts) and current (amperes). Combined with Ohm's law V = I × R, two more equivalent expressions follow: P = I² × R (useful when current and resistance are known) and P = V² / R (useful when voltage and resistance are known).
The calculator reads whichever two fields you fill in, then solves the remaining two using the appropriate formula. For example, filling in V and R gives I = V/R and P = V²/R; filling in P and R gives I = √(P/R) and V = √(PR). All four quantities must be strictly positive (entering zero would imply no circuit or undefined results).
This model covers DC circuits and the time-averaged (RMS) power in purely resistive AC circuits. For reactive (capacitive or inductive) AC loads, real power P = V·I·cos(φ) where φ is the phase angle — that apparent vs reactive power distinction is outside the scope of this calculator.
Frequently asked questions
Power (watts) is the rate of energy conversion — how fast energy is used. Energy (joules or kilowatt-hours) is power multiplied by time. A 100 W light bulb left on for 1 hour consumes 0.1 kWh of energy.
Yes, for purely resistive AC loads — enter RMS voltage and RMS current. For loads with inductors or capacitors, the apparent power S = V·I is larger than the real (active) power P = V·I·cos(φ). This calculator computes real power only; use a power-factor calculator for reactive loads.
Zero voltage with non-zero current, or zero resistance with non-zero voltage, implies an impossible ideal short circuit. Zero current means no power and nothing to solve. The calculator requires all quantities to be positive and finite.
Also known as
TG we-Calculate Editorial Team. (2026). Electrical Power Calculator — P, V, I, R Solver [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/electrical-power-calculator
TG we-Calculate Editorial Team. "Electrical Power Calculator — P, V, I, R Solver." TG we-Calculate. 2026. https://we-calculate.com/calculator/electrical-power-calculator.
TG we-Calculate Editorial Team, "Electrical Power Calculator — P, V, I, R Solver," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/electrical-power-calculator
@misc{wecalculate_electrical_power_calculator, title = {Electrical Power Calculator — P, V, I, R Solver}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/electrical-power-calculator}}, year = {2026}, note = {TG we-Calculate} }
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