Ohm's law (V=IR) alone relates three quantities — voltage, current, and resistance. But add power (P=VI) and its algebraic derivatives, and any two of all four values determine the other two. Know current and power but not voltage or resistance? V=IR by itself can't get you there — you need the power equation too.
Power wheel calculator, all four values covered
Rather than making you pick from six possible combinations in a dropdown, this calculator just watches which two of the four fields — voltage, current, resistance, power — you've filled in, and solves for the other two automatically.
How to calculate watts from current and resistance
Fill in current and resistance and power comes out as I²R automatically — no need to remember which derived formula applies to which pair of known values.
Voltage current resistance calculator, three or more values
Filling in three or four fields shows a message asking you to clear one — with three values you might be describing an inconsistent circuit, so it doesn't guess which one to trust.
