Enter any two of voltage, current and resistance, leaving the third blank, to solve for the missing value using Ohm's Law (V = I × R), along with power.
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Ohm's Law states that voltage equals current multiplied by resistance: V = I × R. This calculator rearranges the formula depending on which value you leave blank: current = voltage ÷ resistance, or resistance = voltage ÷ current. Power is then calculated as voltage × current (P = VI) using the completed set of values.
Enter voltage 12 and resistance 4, leaving current blank: current = 12 ÷ 4 = 3 amps, and power = 12 × 3 = 36 watts. If instead you entered voltage 12 and current 3 (leaving resistance blank), the calculator would solve resistance = 12 ÷ 3 = 4 ohms, arriving at the identical complete set of values either way, since any two of the three values fully determine the third.
Filling in all three fields at once, the calculator needs exactly one field left blank to know which value to solve for, if all three are filled it can't tell which one you actually want calculated.
Entering resistance as zero when solving for current, dividing voltage by zero resistance is undefined (a short circuit in practice), the calculator will flag this rather than return an answer.
Forgetting that power depends on the completed set of all three values, not just two, if you only intended to check voltage and current, the resistance value shown is still a real, calculated part of the answer, not a placeholder.
Leave exactly one field blank, the one you want to solve for. If all three are filled in, the calculator will ask you to leave one blank.
You need at least two of the three values (voltage, current, resistance) filled in for the calculator to solve for the third.
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