Ohm’s Law Calculator
This Ohm's law calculator solves voltage, current, resistance, or power using the formula for Ohm's law, V = IR. Enter any two values and the Ohm's law calculator finds the rest, including power. It applies the Ohm's law equation and the current, voltage and resistance formula in one step.
Enter any two of the three values; the third and the power are calculated automatically.
Results
The Ohm’s Law Calculator is part of our DC/AC Circuits collection. Browse more dc/ac circuits to size, convert, and check your work alongside this tool.
What the Ohm's law calculator does
The Ohm's law calculator applies the most important relationship in electronics. The formula for Ohm's law ties voltage, current, and resistance together, and this ohm's calculator solves whichever one you are missing. Enter two values and the Ohm's law calculator returns the third plus the power, so you never rearrange the current resistance voltage formula by hand.
Formula for Ohm's law
The formula for Ohm's law is a single equation with three arrangements:
This current, voltage and resistance formula is the Ohm's law equation. The Ohm's law calculator also finds power with P = V × I, covering the ohm's law formula for power too.
Ohm's law calculator example
A 12 volt supply across a 6 ohm load, using the formula for Ohm's law:
The Ohm's law calculator then finds power: P = 12 × 2 = 24 W. Enter 12 and 6, leave current blank, and the ohm's calculator returns exactly these.
How to use the Ohm's law calculator
Enter the two values you know among voltage, current, and resistance, then leave the third blank. The Ohm's law calculator detects the missing value and solves it with the Ohm's law equation, showing the power underneath. As an ohm's law resistance calculator, enter voltage and current and read the resistance directly.
Reading the Ohm's law calculator result
Each output has a use. The current tells you what your components and wiring must carry. The resistance from the ohm's law resistance calculator shows how much a part opposes current. The power figure is the one people forget: resistors have a wattage rating, so if the Ohm's law calculator shows power near that rating, pick a bigger part.
When to use the Ohm's law calculator
- Sizing an LED resistor with the formula for Ohm's law
- Finding current from the current, voltage and resistance formula
- Checking a part with the ohm's law resistance calculator
- Working out dissipation with the ohm's law formula for power
Common Ohm's law mistakes
- Mixing units. The formula for Ohm's law needs volts, amps, and ohms; milliamps or kilohms without converting throw it off.
- Ignoring power. The Ohm's law calculator shows power for a reason; a resistor with the right resistance can still burn out.
- Applying V=IR to diodes. Non-ohmic parts do not follow the Ohm's law equation in a straight line.
Tips for accurate Ohm's law results
- Convert everything to volts, amps, and ohms first.
- Check the power figure as a sanity test on your inputs.
- Size resistors for at least twice the power the ohm's law formula for power reports.
Understanding the formula for Ohm's law
To get the most from the Ohm's law calculator, picture the water analogy. Voltage is the pressure pushing water through a pipe, current is the flow rate, and resistance is how narrow the pipe is. Raise the pressure and more flows; narrow the pipe and less gets through. The formula for Ohm's law captures this exactly, which is why the current, voltage and resistance formula feels intuitive once the analogy clicks.
Series and parallel with the Ohm's law calculator
Real circuits rarely have one resistor, so the Ohm's law calculator is most useful after you combine them. Resistors in series add up; resistors in parallel combine to less than the smallest one. Reduce the network to a single resistance, then the Ohm's law equation gives the total current. This combine-then-solve routine, powered by the ohm's calculator, is the foundation of all circuit analysis, and it is why learning the formula for Ohm's law early pays off across every later topic.
Ohm's law formula chart
The four quantities the Ohm's law equation links:
| Quantity | Symbol | Formula |
|---|---|---|
| Voltage | V | V = I×R |
| Current | I | I = V÷R |
| Resistance | R | R = V÷I |
| Power | P | P = V×I |
Ohm’s Law Calculator FAQ
What is the formula for Ohm's law?
The formula for Ohm's law is V = IR, voltage equals current times resistance. The Ohm's law calculator rearranges it to I = V/R or R = V/I to solve whichever value you need.
How do I find resistance?
Divide voltage by current. The ohm's law resistance calculator does this when you enter voltage and current and leave resistance blank, applying R = V/I.
What is the Ohm's law formula for power?
Power equals voltage times current, P = V × I. The Ohm's law calculator shows the power automatically once two of the three values are known.
Does the Ohm's law calculator work for AC?
For resistive AC loads, yes. When a circuit has capacitors or inductors you replace resistance with impedance, but the formula for Ohm's law still holds for resistive calculations.