Ohm’s Law Calculator
Calculate current and power from voltage and resistance using Ohm’s law.
Interactive Electrical Calculator
Ohm’s Law Calculator
Calculate current and power from voltage and resistance using Ohm’s law.
Result
Enter values and calculate.
About the Ohm’s Law Calculator
The Ohm’s Law Calculator handles the basic Ohm's-law relationships between voltage, current and resistance without needing a spreadsheet, app download or manual lookup table. Calculate current and power from voltage and resistance using Ohm’s law. Almost every other calculator on this site builds on the same handful of relationships between voltage, current, resistance and power — getting comfortable with them makes the rest of electrical work easier to reason about.
It's aimed at students, hobbyists and anyone who needs a quick, reliable check of a basic electrical relationship, who need a fast, reliable number without redoing the math by hand each time.
How the calculation works
Behind the scenes, the calculation follows:
I = V / R; P = V × I.
Where each input maps to a field in the calculator above:
- Voltage in V.
- Resistance in Ω.
Change any field above and the result recalculates immediately — nothing is submitted anywhere, so it's safe to experiment freely.
A worked example
For example, start with 12 V for voltage and 10 Ω for resistance. That's a reasonable starting point to explore from: nudge one value up or down and watch how much the result shifts before you commit to a final design figure.
When to use the Ohm’s Law Calculator
Typical reasons people reach for the Ohm’s Law Calculator:
- Checking a homework or exam answer against a quick independent calculation.
- Verifying a component value before it goes into a circuit.
- Working backward from a measured voltage and current to find an unknown resistance.
- Building intuition for how voltage, current and resistance move together before tackling a more complex calculator.
Good practice: These calculators assume ideal, linear conditions — real components have tolerances, temperature effects and non-linear behavior that a simple formula does not capture.
Also worth knowing: Ohm's law (V = I × R) and the power law (P = V × I) are the two relationships nearly every other electrical calculation is built from.
Frequently asked questions
What does the Ohm’s Law Calculator calculate?
Calculate current and power from voltage and resistance using Ohm’s law.
Can I rely on this number for a real installation?
The formula above is applied exactly to the values you enter, so the math itself is precise. Real-world results can still differ due to component tolerances, temperature, installation method, equipment efficiency and local code requirements, so treat the output as a strong planning estimate and verify final designs against manufacturer data and the electrical code that applies to your installation.
Do I need to sign up or install anything to use it?
No sign-up, download or installation is needed. The Ohm’s Law Calculator runs entirely in your browser and is free to use.
What happens if I get this wrong?
These relationships apply identically in AC and DC circuits (with power factor and phase added for AC), which is why they show up in almost every branch of electrical work.
Will this work for both metric and everyday values?
The Ohm’s Law Calculator works on any modern browser, phone or desktop, and recalculates as soon as you press Calculate. If a result looks off, double-check that every field is filled in with the unit shown next to it (mixing up units, such as W with kW, is the most common cause of an unexpected answer) and re-enter the values.