CalcStack — free, instant, no signup. The interactive calculator loads automatically.
Any two in, the other two out.
Ohm's law and the power law form the four equations behind every circuit: V = IR and P = VI. Knowing any two of voltage, current, resistance, and power determines the other two — but the rearrangements are where homework and field work slow down. This calculator does all twelve permutations: pick your two knowns, read everything else.
Students checking homework, hobbyists sizing resistors for LED projects, electricians and automotive techs doing quick field math. People use it because the rearrangements (solve for R, solve for P) are where errors creep in — and a wrong resistor size can mean a burnt circuit.
V = IR: voltage equals current times resistance. It says pushing more current through a resistance requires proportionally more voltage — the foundational relationship of all circuit analysis.
P = V²/R. A 12 V supply across 6 Ω dissipates 24 W. The calculator handles this and all other rearrangements automatically — pick the "Voltage & Resistance" mode.
For purely resistive AC loads using RMS values, yes. With capacitors or inductors, impedance replaces resistance and phase enters the math — this calculator covers the DC and resistive-AC cases, which includes most household and automotive work.