numvana

Ohm's Law Calculator

Solve for voltage, current, or resistance from the other two using Ohm's law, with power calculated automatically.

Voltage (V)
12 V
Current (I)
2 A
Resistance (R)
6 Ω
Power (P)
24 W

How it works

Ohm's law relates voltage, current, and resistance in a circuit as V = I × R. Pick which quantity to solve for; the calculator rearranges that same identity to find it from the other two — I = V ÷ R when solving for current, or R = V ÷ I when solving for resistance — and ignores whatever placeholder value is in the field you're solving for.

Power is then always P = V × I, computed from the final, consistent set of all three values, not from whatever was typed into that field beforehand.

Resistance can't be negative for a passive component (a plain resistor, wire, or similar), so this calculator rejects a negative resistance value and any voltage/current combination that would imply one.

FAQ

Why does the calculator ask which quantity to solve for instead of just three blank fields?

Ohm's law only has two independent quantities among voltage, current, and resistance — the third is always determined by the other two. Asking which one to solve for avoids the ambiguity of a user entering all three at once with values that don't actually satisfy V = I × R.

Why is resistance required to be zero or positive?

A real passive resistor can't have negative resistance — it doesn't add energy to a circuit, only dissipate it. If you're solving for resistance and the entered voltage and current would imply a negative value, that's a sign one of the inputs has the wrong sign for the circuit you're modeling.

Related calculators