formula
Ohm's Law Formula Explained
Complete Ohm's Law formula reference with variables, units, and examples.
V = IR
This reference explains the Ohm's Law formula used by our free Ohm's Law Calculator. Use it to understand variables, units, and common mistakes before you calculate.
The formula
V = IR
Variables and units
- V — Voltage (potential difference) (volts (V))
- I — Current (amperes (A))
- R — Resistance (ohms (Ω))
Worked example
Inputs: V = 12 V, R = 4 Ω — find current
- I = V ÷ R
- I = 12 ÷ 4 = 3 A
Result: Current = 3 amperes
When to use this formula
Use this formula when you need a quick ohm's law estimate with values you already know. Our Ohm's Law Calculator applies the same relationship automatically so you can verify handwritten work.
Common mistakes
- Mixing milliamps with amps without converting
- Using total resistance incorrectly in parallel vs series circuits
- Applying Ohm's law to non-ohmic devices like diodes
Frequently asked questions
What formula does the Ohm's Law Calculator use?
It uses: V = IR. Enter your values and the calculator returns the result with the same relationship.
Can I use different units?
Check the calculator field labels for expected units. Convert inputs before calculating if your data uses different units.
Is the Ohm's Law Calculator free?
Yes. It runs entirely in your browser with no account required.
Try the calculator
Ohm's Law Calculator