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Ohm's Law Calculator

Enter any two electrical values to instantly calculate the other two. Covers Voltage (V), Current (I), Resistance (R) and Power (P).

Formula Reference
V = I × R  |  V = P / I  |  V = √(P×R)
I = V / R  |  I = P / V  |  I = √(P/R)
R = V / I  |  R = V² / P  |  R = P / I²
P = V × I  |  P = I² × R  |  P = V² / R
Enter any two values (leave the others blank)

The tool will calculate the remaining two automatically.

Voltage (V)
Current (I)
Resistance (R)
Power (P)

Ohm's Law: V = I × R. Power extension: P = V × I = I² × R = V²/R. These four equations let you calculate any electrical quantity when two others are known. The law applies to resistive (DC) circuits and resistive AC circuits.

P = V × I. A 230V appliance drawing 5A consumes 1,150 W = 1.15 kW. For AC with reactive loads, Real Power (W) = V × I × cos(φ), where cos(φ) is the power factor.

Ohm's Law (V = IR) applies directly to DC and purely resistive AC circuits. For AC with reactive loads, V = I × Z where Z is impedance (combining resistance, inductance and capacitance). This calculator uses the resistive/DC form.