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Ohms Law Calculator

Calculate voltage, current, resistance, and power with Ohm's law. Enter any 2 of the four DC values (V, I, R, P) and press Calculate to get the other two, with the formula solution shown. An AC section handles impedance, current, voltage, and complex power as magnitude ∠ phase angle or in rectangular R + jX / P + jQ form. Everything runs locally in your browser.

DC — enter 2 of V / I / R / P

AC — enter 2 as magnitude ∠ angle° or R + jX / P + jQ

STEP 1

Fill in any 2 DC values

Type a number into exactly two of Voltage, Current, Resistance, and Power, and pick a unit per field — volts from microvolts (μV) to megavolts (MV), current from μA to MA, resistance in Ω / kΩ / MΩ, power from μW to MW. The other two fields must stay empty.

STEP 2

Press Calculate

The two missing quantities appear in base units (V, A, Ω, W) together with the solution lines, e.g. I = V / R = 20 / 10 = 2 A. Copy the results, or press Reset to clear and start over.

STEP 3

Use the AC section for phasors

For AC circuits, enter any 2 of impedance Z, current I, voltage V, and complex power S as magnitude ∠ phase angle in degrees — or type Z as R + jX and S as P + jQ — and Calculate returns the missing phasors in polar and rectangular form.

Ohm's law calculation formulas

Ohm's law — current formula: The current I in amps (A) is equal to the voltage V in volts (V) divided by the resistance R in ohms (Ω): I = V / R. Example: I = 20V / 10Ω = 2A.
Electric power formula: The power P in watts (W) is equal to the voltage V in volts (V) times the current I in amps (A): P = V × I. Example: P = 20V × 2A = 40W. Combined with Ohm’s law this also gives P = V²/R = I²R.
Which 2 values should I enter?: Any exactly-two combination of V, I, R, and P works: V+R gives I = V/R and P = V²/R; V+I gives R = V/I and P = V×I; V+P gives I = P/V and R = V²/P; I+R gives V = I×R and P = I²R; I+P gives V = P/I and R = P/I²; R+P gives V = √(P×R) and I = √(P/R). Entering fewer or more than 2 values is reported as an error.
AC Ohm’s law formula: For AC circuits the voltage phasor V in volts is equal to the current phasor I in amps times the impedance phasor Z in ohms: V = I × Z, i.e. magnitudes multiply and phase angles add: V = (|I| × |Z|) ∠ (θI + θZ). Impedance is often entered as magnitude ∠ angle or as R + jX (resistance plus reactance).
Complex power S in volt-amps: The complex power S in volt-amps (VA) is S = (|V| × |I|) ∠ (θV − θI). Its real part is the real power P in watts and its imaginary part is the reactive power Q in volt-amps reactive (var), which is why S can be entered directly as P + jQ.
What do the unit prefixes mean?: micro (μ) = ×10⁻⁶, milli (m) = ×10⁻³, kilo (k) = ×10³, mega (M) = ×10⁶. For example 1 kΩ = 1000 Ω and 500 mA = 0.5 A. All results are shown in base units (V, A, Ω, W, VA).

Privacy: every calculation runs in your browser tab — no value you type is sent anywhere. Copy result uses your clipboard only. Results assume ideal ohmic/resistive DC values and balanced sinusoidal AC phasors; verify real installations with a multimeter.