---
title: "Ohm's law calculator — free, runs in your browser"
description: "Voltage, current, resistance and power — give any two, get the other two. Free, no sign-up, and nothing you enter leaves your browser."
url: https://atoneplace.net/tools/ohms-law-calculator/
site: "At One Place"
---

# Ohm's law calculator

Voltage, current, resistance and power — give any two, get the other two.

## How it works

Enter any two of voltage, current, resistance and power, and this gives the remaining two. V = IR, and P = VI, which combine into the twelve forms of the Ohm’s law wheel.

Power is the one people forget to check, and it is usually what fails. A resistor sized correctly for its resistance can still burn out if the power dissipated exceeds its rating — a quarter-watt resistor passing 100 mA at 5 V is dissipating half a watt and will not survive.

Ohm’s law describes ohmic conductors, which is most wire and most resistors under normal conditions. It does not describe diodes, transistors, filament lamps at varying temperature, or anything else whose resistance changes with the current through it.

> This tool runs entirely in your browser. Nothing you enter is sent to a server, logged or stored, and the page keeps working with the network disconnected.

## Common questions

### What is Ohm’s law?

V = IR — voltage equals current times resistance. Combined with P = VI it gives every relationship between the four quantities.

### Does Ohm’s law apply to everything?

No. It describes ohmic conductors. Diodes, transistors and filament lamps all have resistance that varies with conditions, so it does not hold for them.

### Why does my resistor get hot?

It is dissipating more power than its rating. Check P = I²R against the resistor’s wattage, not just its resistance.

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## Sources

- Calculated on this page — At One Place (/about/)