Find voltage, current, resistance, or power from any two of the other three — free and instant.
Ohm's Law (V = IR) and the power formula (P = VI) together relate voltage, current, resistance, and power — knowing any two of the four lets you find the other two. This tool works in whichever direction you need: enter voltage and current to find resistance and power, or resistance and power to find voltage and current, and so on.
The two fields you've most recently edited are treated as the known values, and the other two update to match — the same way a real "solve for the missing value" calculator should work, rather than forcing you into one fixed direction.
All combinations of positive voltage, current, resistance, and power are mathematically consistent with each other — there’s no invalid combination the way there can be with, say, a triangle’s side lengths.
Current and voltage can be negative to represent direction, but resistance and power are conventionally treated as positive — this tool expects positive resistance and power.
They’re the same relationship written two ways — substituting V=IR into P=VI gives P=I²R, and substituting I=V/R gives P=V²/R. All three are used depending on which two quantities you already know.