Ohm's Law Calculator (Voltage, Current, Resistance, Power)

Voltage, current, and resistance, plus the power they produce

At 12 volts and 2 amps (with resistance left at 0 to mark it unknown), Ohm's Law solves resistance as 6 ohms (V / I = 12 / 2), and the resulting power is 24 watts (P = V x I = 12 x 2).

Ohm's Law (V = I x R) is one of the most fundamental relationships in basic electronics, and like the other physics solve-for-the-unknown tools here, it rearranges depending on which variable is missing: resistance = voltage / current, or current = voltage / resistance.

Power (24 watts) is calculated as a bonus fourth value beyond the core three-variable Ohm's Law relationship -- P = V x I is a separate but closely related formula, useful for immediately seeing how much energy per second a circuit with these voltage and current values is actually dissipating or consuming.

Why exactly two of the three main values must be set

Exactly two of V, I, R must be nonzero. Power is V times I. This calculator requires exactly two of voltage, current, and resistance to have real nonzero values -- with only one known value, Ohm's Law alone doesn't provide enough information to solve for both of the others, since there are genuinely two unknowns and only one equation relating all three.

Power can also be expressed using other equivalent formulas once you know any two of the three main values -- P = I² x R or P = V² / R would give the identical 24-watt answer here, since all these formulas are just different algebraic rearrangements of the same underlying relationships.

This models a simple resistive circuit -- purely resistive loads follow Ohm's Law directly, but circuits with capacitors or inductors (which introduce frequency-dependent reactance) require more advanced AC circuit analysis beyond this basic DC-style relationship.

Related electronics tools

Once you know a resistance value like the 6 ohms solved here, the Resistor Color Code Calculator helps identify or verify a physical resistor with that approximate value from its color bands.

For a related but different passive component, the Capacitor Value Code Converter decodes a capacitor's printed value marking instead.

Frequently Asked Questions (FAQ)