Enter any two of voltage, current, and resistance to solve for the third using Ohm's Law, plus see the resulting power.
How to Use the Ohm's Law Calculator
Fill in any two of voltage, current, and resistance and leave the third blank — the calculator solves for whichever's missing automatically, rather than needing you to pick which rearrangement of the formula applies.
Three quantities, one relationship, and knowing any two hands you the third for free. Ohm's Law is arguably the first thing anyone learns in electronics, and it stays useful for the rest of a career — from sizing a resistor for an LED to sanity-checking a reading off a multimeter.
V = I × RV is voltage in volts, I is current in amperes, R is resistance in ohms. Rearrange it depending on what you're missing:
Current: I = V ÷ R
Resistance: R = V ÷ IThis calculator picks the right rearrangement automatically based on which field you've marked as unknown.
Power comes along for free once you have voltage and current: P = V × I. Swap in Ohm's Law and you get two more versions of the same relationship — P = I²R when you know current and resistance, P = V²÷R when you know voltage and resistance. Same physical quantity, three different-looking formulas depending on what's sitting in front of you.
One caveat worth knowing: Ohm's Law is exact for ohmic components — resistors, most wire, conductors that hold a constant resistance regardless of what's flowing through them. Diodes, LEDs, and transistors don't play by that rule; their resistance shifts with voltage and current, so V = IR gives you an approximation for those parts, not a precise answer.