Interactive Reference
Ohm's Law Wheel
The wheel shows every way to find Voltage, Current, Resistance, and Power from any two of the others. Each quarter of the wheel solves for one quantity (V, I, R, or P), and the three segments in that quarter are the three formulas for it — depending on which two values you already know. Click any segment, or any formula card, to open a calculator that shows the full worked solution.
V — Voltage (volts)
I — Current (amps)
R — Resistance (ohms)
P — Power (watts)
Ohm's law works in AC and DC — but AC reactive circuits use impedance (Z), not just R.(tap to expand)
It's the same law either way; the only thing that changes is what opposes the current. In a DC or purely resistive circuit that's just resistance (R). AC circuits with capacitors or inductors add reactance (which depends on frequency), and resistance plus reactance together is called impedance (Z) — also measured in ohms. So for those AC circuits you use V = I × Z instead of V = I × R. (When there's no capacitance or inductance, Z equals R and the two are identical.) This wheel uses plain R, so for AC circuits with reactive parts reach for impedance & matching or the reactance / filter tools.
Click any segment to select a formula
Select a formula segment from the wheel above or a card below to open the calculator.
All 12 Formulas