Ohm's Law Calculator
Enter any two known values to solve for voltage, current, resistance, and power. Works with any combination of V, I, R, and P.
Power Formulas Used
How to Use the Ohm's Law Calculator
Solve for any electrical value in three simple steps.
Enter Two Values
Type in any two of the four fields: Voltage (V), Current (I), Resistance (R), or Power (P). The calculator accepts any combination.
Click Calculate
Press the Calculate button and the tool instantly solves for all missing values using Ohm's law (V = I × R) and the power formula (P = V × I).
Read Color-Coded Results
Results are displayed with color coding: red for voltage, blue for current, green for resistance, and orange for power. Units shown in each card.
Ohm's Law Formula Reference
Common Ohm's law formulas used in electrical engineering.
| Formula | Description | Unit |
|---|---|---|
| V = I × R | Voltage equals current times resistance | Volts (V) |
| I = V / R | Current equals voltage divided by resistance | Amperes (A) |
| R = V / I | Resistance equals voltage divided by current | Ohms (Ω) |
| P = V × I | Power equals voltage times current | Watts (W) |
| P = I² × R | Power equals current squared times resistance | Watts (W) |
| P = V² / R | Power equals voltage squared divided by resistance | Watts (W) |
Frequently Asked Questions
Common questions about Ohm's law and electrical calculations.
Ohm's law states that the current through a conductor between two points is directly proportional to the voltage across the two points. The mathematical relationship is V = I × R, where V is voltage in volts, I is current in amperes, and R is resistance in ohms.
Power can be calculated using P = V × I (voltage times current). You can also use P = I² × R (current squared times resistance) or P = V² / R (voltage squared divided by resistance). All three formulas give the same result.
If the values you enter are mathematically inconsistent (e.g., you enter V=10, I=5, R=1), the calculator uses the most recently entered pair to compute the other values. A warning will indicate which pair was used for calculation.
The V/IR triangle is a mnemonic device. Cover the variable you want to find and the remaining two show the formula. For example, cover V and you see I × R. Cover I and you see V / R. Cover R and you see V / I.
This calculator uses DC Ohm's law which applies to purely resistive AC circuits. For AC circuits with reactive components (inductors or capacitors), you need to account for impedance and phase angle using complex numbers.