# Ohm's Law Calculator

> Calculate ohm's law step by step: V = I × R.

Page: https://freecalculator.tech/tools/ohms-law-calculator
Last reviewed: 2026-11-03

## Formula

V = I × R. Rearranged: I = V ÷ R and R = V ÷ I. Power is also shown as P = V × I.

- Ohm's law applies to ohmic (linear) conductors at a steady temperature.
- Dividing by zero is blocked: resistance must be above zero to solve for current, and current must be non-zero to solve for resistance.
- Units are volts, amperes and ohms; enter mA as 0.001 A and kΩ as 1000 Ω.
- V = I × R. Rearranged: I = V ÷ R and R = V ÷ I. Power is also shown as P = V × I.
- Inputs used: Solve for, Voltage, Current, Resistance.

## Inputs

- Solve for
- Voltage
- Current
- Resistance

## Worked example: 12 V across 6 Ω

Find the current through a 6 Ω resistor on a 12 V supply.
1. I = V ÷ R = 12 ÷ 6 = 2 A.
2. P = V × I = 12 × 2 = 24 W.

## Common questions

### Does Ohm's law work for LEDs and diodes?

Not directly. Diodes are non-linear, so their resistance changes with current. Use the LED resistor calculator, which subtracts the LED's forward voltage first.

### Can I use it for AC circuits?

For purely resistive AC loads, yes, using RMS voltage and current. With motors, coils or capacitors you need impedance instead of resistance, and power factor matters.

### Why does the power figure matter?

Every resistor has a power rating. If V × I exceeds that rating the part overheats, so pick a resistor rated comfortably above the calculated power.

### How do I use the Ohm's Law Calculator?

Enter the required values for Solve for, Voltage, Current, Resistance. The calculator applies the formula on this page and shows the main result with any supporting breakdown so you can check the arithmetic.

### What formula does the Ohm's Law Calculator use?

V = I × R. Rearranged: I = V ÷ R and R = V ÷ I. Power is also shown as P = V × I. The visible formula section above lists the calculation path and the edge cases the page handles, so the result can be checked without relying on the form alone.

### Can the Ohm's Law Calculator be used for exact decisions?

Use it as a calculation aid, not as a substitute for checking the underlying rule, contract, policy, or professional advice that applies to your situation. When a result depends on local rules, personal details, prices, or dates, enter those values yourself and confirm them before acting.

## Limitations and assumptions

- Assumes a constant resistance; real resistance rises or falls with temperature.
- Ignores wire, contact and internal source resistance.
- For AC with reactive loads, impedance and phase angle are not modelled.
- Results are estimates for planning and learning. Real designs, installations and bids must be checked by a qualified, licensed professional against the codes that apply where you work.
- The result depends on the values you enter for this ohm's law calculator; it does not supply missing rates, rules, prices, dates, or assumptions for you.

## Sources

- OpenStax (Rice University) — https://openstax.org/details/books/university-physics-volume-2

## Cite this page

- APA: Free Calculator. (2026, November 3). Ohm's Law Calculator. https://freecalculator.tech/tools/ohms-law-calculator
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