Enter any two of voltage, current, resistance, or power — the other two are calculated instantly with unit selectors.
Enter any two values — the other two are calculated automatically.
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Quick answers to common questions
Ohm's Law states V = I × R, where V is voltage (volts), I is current (amps), and R is resistance (ohms). Rearranged: I = V/R (find current) or R = V/I (find resistance). Example: a 12V circuit with 4Ω resistance draws I = 12/4 = 3 amps of current.
Power (watts) = Voltage × Current (P = VI). Combined with Ohm's Law, this gives two more useful formulas: P = I²R (power from current and resistance) and P = V²/R (power from voltage and resistance). This calculator lets you enter any two known values across V, I, R, and P to solve for the rest.
Ohm's Law describes ideal resistive circuits. Real-world components (like LEDs, motors, or heating elements) may not follow a purely linear V-I relationship, so calculated values are theoretical. Always account for a component's actual datasheet ratings, not just the Ohm's Law result, when designing real circuits.
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