Enter any two values. Leave the others blank to solve for them.
All 12 Ohm's Law Formulas
From V and I: R = V/I, P = V*I. From V and R: I = V/R, P = V^2/R. From V and P: I = P/V, R = V^2/P. From I and R: V = I*R, P = I^2*R. From I and P: V = P/I, R = P/I^2. From R and P: V = sqrt(P*R), I = sqrt(P/R). Enter any two known values and the calculator selects the appropriate formula pair.
Frequently Asked Questions
Ohm's Law states that the current through a conductor is directly proportional to the voltage and inversely proportional to the resistance: I = V / R. Georg Ohm published this relationship in 1827. It applies to purely resistive circuits and is fundamental to all electrical and electronics engineering.
The four electrical quantities are related by: V = I x R (voltage = current x resistance). I = V / R (current = voltage / resistance). R = V / I (resistance = voltage / current). P = V x I = I^2 x R = V^2 / R (power in all three forms).
The Ohm's Law wheel (or Ohm's Law triangle) is a visual aid showing all the possible formulas relating V, I, R, and P. It lets you quickly identify which formula to use based on which two values you know. This calculator implements all 12 formula variations.
Ohm's Law in its basic form (V = IR) applies to AC circuits with purely resistive loads. For AC circuits with inductors and capacitors, the concept is extended to impedance (Z) using complex numbers: V = I x Z. Impedance accounts for both resistance and reactance.
Voltage is measured in Volts (V), current in Amperes or Amps (A), resistance in Ohms (Ω), and power in Watts (W). Common prefixes: mA (milliamps, 1/1000 A), kΩ (kilohms, 1000 Ω), mW (milliwatts, 1/1000 W), kW (kilowatts, 1000 W).
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