Ohm's Law Calculator
Solve any one of voltage, current, resistance, or power from the other two using the Ohm's law wheel formulas (V=IR, P=VI, P=I²R, P=V²/R).
V
A
Ω
W
Results
Computed Value
Enter 2+ values
Known Values
None yet — enter at least two quantities.
Derived Values
Power (P = V·I)
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Power (P = I²·R)
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Power (P = V²/R)
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What is Ohm's Law?
Ohm's law states that the current through a conductor between two points is directly proportional to the voltage across those points. Combined with the power formulas, it lets you solve for any one quantity in a circuit when two others are known.
P = V × I
P = I² × R
P = V² / R
The Ohm's Law Wheel
Example
Leave one field blank and enter the others. For instance, if you know a 12 V supply drives 3 A, then R = 12/3 = 4 Ω and P = 12 × 3 = 36 W. Enter any two of V, I, R, P and the calculator finds the missing values.
Common Use Cases
- Choosing a resistor to limit current to a safe level in an LED circuit.
- Estimating power dissipation to select an appropriately rated resistor.
- Designing and troubleshooting DC electronic circuits.
- Verifying component specifications against an unknown value.
FAQs
How many fields do I need to fill in?
Fill in any two of the four quantities — voltage (V), current (I), resistance (R), or power (P) — and the calculator determines the rest. Leave the unknown field blank.
Does Ohm's law apply to AC circuits?
This calculator assumes DC circuits. In AC circuits with reactive components (capacitors, inductors), impedance replaces simple resistance and phase angles come into play, so these formulas are only directly applicable for resistive AC loads like heaters or incandescent bulbs.
What if I enter values that don't match?
The calculator treats the blank field as the one to solve for. If the entered values are internally inconsistent, the result will simply reflect the combination you supplied — double-check your units (ohms, amps, volts, watts).