How to use the Ohm’s law calculator
- 1
Enter two values
Fill in any two fields, e.g. voltage and resistance.
- 2
Read the results
Current and power are calculated as you type.
- 3
Change any value
Typing in a third field replaces the oldest one, so two values always stay given.
Why use this Ohm’s law calculator?
All four quantities
Solves voltage, current, resistance and power from any pair – 12 formulas in one.
Instant and private
Results update as you type; nothing is sent anywhere.
Free, no sign-up
No account, no ads in the way, works on phone and desktop.
Formulas shown
The page explains how each result is calculated, so you can check it.
Popular uses
- Sizing resistors
- Checking power supplies
- Fuse and wire sizing
- Arduino and ESP32 projects
- Electronics homework
- Heater and load calculations
Frequently asked questions
What is Ohm’s law?
Ohm’s law says that the voltage across a resistor equals the current through it times its resistance: V = I × R. Electrical power is P = V × I, so P = I² × R = V² / R.
How do I calculate current from voltage and resistance?
Divide the voltage by the resistance: I = V / R. For example 12 V across 6 Ω gives 2 A.
How do I calculate power?
Multiply voltage and current: P = V × I. 12 V at 2 A is 24 W.