Power Calculator
Calculate electric power, voltage, current, and resistance. The DC calculator solves any two of resistance (Ω), current (A), voltage (V), and power (W); the AC calculator works with impedance, phase angles, complex power S = P + jQ and power factor; the energy calculator gets average power from energy and time (P = E / Δt). Everything runs locally in your browser.
DC power calculator
Enter 2 values (R, I, V, P) to get the other two, then press Calculate.
AC power calculator
Enter 2 magnitudes + 2 phase angles (degrees) to get the other values. Blank angle = 0°.
Energy & power calculator
P(W) = E(J) / Δt(s) — enter 2 values to get the other one.
Pick the calculator
Use DC power for resistive circuits, AC power for impedances with phase angles (Ω ∠ °, VA ∠ °), or Energy & power when you know the energy consumed in joules over a time period in seconds.
Enter exactly two values
Each calculator needs 2 values and calculates the other values. Choose a unit prefix per row (μA…MA, μV…MV, μW…MW, Ω/kΩ/MΩ); for AC also type the phase angles in degrees — a blank angle counts as 0°.
Press Calculate, read the result
The two missing quantities appear with units; the AC result also shows real power P (W), reactive power Q (VAR), power factor |cos φ|, and the rectangular forms Z = R + jX and S = P + jQ. Copy the result or press Reset per section.
Power calculation formulas
- DC power calculation
- The voltage V in volts is equal to the current I in amps times the resistance R in ohms: V(V) = I(A) × R(Ω). The power P in watts is P(W) = V(V) × I(A) = V²(V) / R(Ω) = I²(A) × R(Ω). For example, 2 A through 10 Ω gives V = 20 V and P = 40 W.
- AC power with phase angles
- The voltage V equals current I times impedance Z: V = I × Z = (|I| × |Z|) ∠ (θI + θZ). The complex power S in volt-amps equals V times I: S = V × I = (|V| × |I|) ∠ (θV − θI). For example, 2 A ∠ 0° through 10 Ω ∠ 30° gives V = 20 V ∠ 30° and S = 40 VA ∠ 30°.
- Real power, reactive power, and power factor
- Real power P(W) = V(V) × I(A) × cos φ, reactive power Q(VAR) = V(V) × I(A) × sin φ, where φ = θV − θI is the complex power phase angle; the power factor is PF = |cos φ|. With S = 40 VA ∠ 30°: P ≈ 34.64 W, Q = 20 VAR, PF ≈ 0.866. A negative φ (capacitive load) makes Q negative while PF stays positive.
- What are R + jX and P + jQ?
- They are the rectangular forms of the polar quantities: impedance Z = R + jX (resistance plus reactance) and complex power S = P + jQ (real plus reactive power). The calculator shows both readouts next to the Z and S rows after you press Calculate.
- Average power from energy and time
- The average power P in watts is equal to the energy consumed E in joules divided by the time period Δt in seconds: P(W) = E(J) / Δt(s). For example, 1500 J consumed over 30 s gives P = 50 W.
- Which unit prefixes are supported?
- DC rows accept micro/milli/base/kilo/mega prefixes: Ω, kΩ, MΩ; μA, mA, A, kA, MA; μV, mV, V, kV, MV; μW, mW, W, kW, MW. AC rows use the same magnitudes (Ω/kΩ/MΩ, μA…MA, V/kV/MV) plus VA, kVA, MVA for complex power. The energy row is fixed at joules, seconds, and watts.
Privacy: every calculation runs in your browser tab — no value you type is sent anywhere. Copy result uses your clipboard only. Results assume sinusoidal RMS values and passive-sign convention (Q > 0 for inductive loads); verify real installations with a meter.