Electrical
Solve for voltage, current, resistance, or power from the other two — V = IR and P = VI, for DC circuits and resistive AC loads.
The two input labels change with the chosen unknown. Results update as you type. All calculations run locally in your browser.
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V = I × R, and P = V × I. From those two, every other form follows: I = V ÷ R, R = V ÷ I, P = I² × R, P = V² ÷ R. The "Check" chip recomputes the solved value through the other relation to confirm consistency.
Solve for current with V = 12 V and R = 4 Ω: I = V ÷ R = 12 ÷ 4 = 3.00 A. Power = V × I = 12 × 3 = 36.00 W. Check through the other form: P = V² ÷ R = 144 ÷ 4 = 36.00 W — consistent.
This is DC and resistive AC: it assumes voltage and current are in phase and resistance is constant. It does not cover reactive AC circuits (inductors, capacitors, phase shift) or temperature-dependent resistance — a filament lamp's resistance rises sharply as it heats, so cold resistance gives a misleading current. Zero resistance means a short circuit: current is unbounded in the ideal model, so the page refuses division by zero rather than showing infinity. Real circuits always have some resistance and a supply with a current limit.
Any two of voltage, current, and resistance determine the third — and power follows from any voltage-current pair. Pick the unknown above and enter the two you know.
Because I = V ÷ R with R = 0 is a short circuit: the ideal model predicts infinite current. Real supplies limit current or fail; no finite answer exists, so the page says so.
For resistive loads (heaters, incandescent lamps) yes, using RMS voltage and current. For motors and electronics with inductance or capacitance, use impedance and phase-aware calculations instead.
A resistor converts power to heat. A 36 W result through a 0.25 W resistor would destroy it — always check the component's power rating against the computed power, not just the resistance value.
Base SI units here: volts, amps, ohms, watts. For milliamps, divide by 1,000 first (500 mA = 0.5 A); for kilohms, multiply by 1,000 (4.7 kΩ = 4700 Ω).
Yes: choose Power and enter voltage and current. The page also shows the implied resistance (V ÷ I) as the check value.
Results are estimates only and do not constitute professional advice.