Updated · Built and checked by the PlinzoTools team, formulas tested against published sources
Solve for voltage, current, or resistance using Ohm's law.
10.0000 V
Ohm's law is the fundamental relationship between voltage, current, and resistance in an electrical circuit. This tool solves for any one of the three, given the other two.
Pick which value to solve for, then enter the other two. The result appears instantly.
V = I × R
Voltage (V, volts) = Current (I, amps) × Resistance (R, ohms)
The calculator has three buttons: Solve voltage, Solve current and Solve resistance. Choosing a mode hides the field you are solving for and shows the other two. Pick the mode that matches the unknown in your circuit, not the one that matches the values you happen to remember. If you are trying to find out how much current will flow through a resistor connected to a battery, choose current and enter the voltage and resistance. If you have measured voltage and current with a meter and want to know an unknown resistor's value, choose resistance.
Solving for current. A hypothetical 12 V supply across a 4 Ω resistor: current = V / R = 12 / 4 = 3 A.
Solving for resistance. A hypothetical 9 V drop measured with 0.5 A flowing: R = V / I = 9 / 0.5 = 18 Ω.
The results are displayed to four decimal places, so a value such as 10 / 3 shows as 3.3333 rather than a tidy fraction. If you need exact fractions, keep the arithmetic by hand.
V = I × R I = V / R R = V / I
When solving for current, resistance cannot be zero, and when solving for resistance, current cannot be zero. In those cases the tool shows its prompt asking for the other values instead of a result. This is not a bug; a true zero-ohm path would in theory draw unlimited current, and a zero-current reading gives no way to determine resistance because any resistance gives zero current at zero voltage. In real circuits, a reading of zero current usually means an open circuit or a switch that is off.
This tool handles DC, or the resistive behavior of simple AC loads. It does not cover reactive components such as inductors and capacitors in AC circuits, where impedance and phase matter. It also does not calculate power, though once you know two values you can find power by multiplying voltage by current. This page is an educational aid. For mains wiring or any work that could shock or start a fire, follow local electrical codes and hire a licensed electrician rather than relying on a quick calculation.
Volts (V) for voltage, amps (A) for current, and ohms (Ω) for resistance.
It applies precisely to "ohmic" components like standard resistors; some components (diodes, transistors) have a non-linear voltage-current relationship where Ohm's law doesn't directly apply.
Current equals voltage divided by resistance, and dividing by zero is undefined, so the tool waits for a non-zero resistance. The same applies to current when solving for resistance.
Convert to base units first. Divide milliamps by 1,000 to get amps, and multiply kilohms by 1,000 to get ohms.
Not directly. Once you have voltage and current from this tool, multiply them to get watts by hand, or divide work by time in the Power Calculator.
Not reliably. Those parts are non-linear, so a single voltage and current pair does not represent a fixed resistance across operating conditions.
Reference: NIST Weights and Measures