Quick start
- Choose the pair of values you know.
- Enter the two values in the labels shown.
- Calculate to get the remaining circuit values.
Best uses
These are the situations this tool is meant for. If your task is close to one of these, the examples and notes below can help you choose the right inputs.
- Find resistance from voltage and current.
- Find current from voltage and resistance.
- Find voltage from current and resistance.
- Estimate power after the core values are known.
What this calculator is solving
The Ohms Law Calculator solves the basic resistor relationships. Enter two known values and it fills in voltage, current, resistance, and power.
You do not need to memorize the formula first. Start by matching each input label on the calculator to the number, date, unit, or setting you actually have.
The formula in plain language
In plain language: The calculator uses V = I x R and P = V x I after the missing voltage, current, or resistance value is solved. The examples on the page are there so you can compare your inputs with a filled-out calculation before copying the answer.
If that sounds abstract, use the example cards on the calculator page. They show a complete set of inputs and the kind of answer you should expect.
How to read the answer
Read the headline result first. Then look at the smaller supporting lines because they explain the parts behind the answer, such as totals, units, ranges, or formula steps.
- Voltage is electrical potential difference.
- Current is flow in amps.
- Resistance is ohms, and power is watts.
Common mistakes to avoid
If the answer looks strange, the most likely cause is a small input mismatch: the wrong unit, date, weight, scale, mode, or policy assumption.
- Do not use simple DC resistor math for every AC or reactive circuit.
- Do not ignore component power ratings and heat.
- Never test live circuits without proper training and equipment.
Research and references
These references shaped the calculator assumptions, unit choices, or safety notes.
Examples from the calculator
6 ohms and 24 W
12 V and 24 W
3 A and 27 W
FAQ in plain language
When should I use the Ohms Law Calculator?
Use it when your task matches one of these common needs: Find resistance from voltage and current. Find current from voltage and resistance. It works best when you already know the values, dates, units, or settings the page asks for.
What is the Ohms Law Calculator doing with my inputs?
In plain language: The calculator uses V = I x R and P = V x I after the missing voltage, current, or resistance value is solved. The examples on the page are there so you can compare your inputs with a filled-out calculation before copying the answer.
What should I double-check before trusting the answer?
This is simple DC or resistive-circuit math. AC circuits, impedance, heat, component ratings, and electrical safety require more care. Also check that you used the right unit, date, scale, or mode because small input changes can change the result.
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Privacy and copying results
Recent answers stay visible only while you work in the current browser tab. They are not sent to a server.
Use Copy answer when you want to paste the expression and result into notes, homework, a message, or another document. Check the units and assumptions before copying.