Ohm’s Law Calculator
Quick answer: Ohm's law says voltage equals current times resistance (V = I × R). If a 12 V supply drives a 4 Ω resistor, the current is 3 A and the power is 36 W. Enter any two values to find the rest.
Use the Ohm’s Law Calculator
Ohm's Law formula and what each symbol means
V = I × R, I = V ÷ R, R = V ÷ I. Power: P = V × I = I² × R = V² ÷ R.
| Symbol | Meaning |
|---|---|
| V | Voltage in volts (V) |
| I | Current in amperes (A) |
| R | Resistance in ohms (Ω) |
| P | Power in watts (W) |
Ohm's Law examples
Find current
V = 12 V, R = 4 Ω. I = 12 ÷ 4 = 3 A. P = 12 × 3 = 36 W.
Find resistance
A 230 V supply drives 2 A. R = 230 ÷ 2 = 115 Ω.
How to calculate Ohm's Law step by step
- Pick the unknown value.
- Choose the matching form of V = IR.
- Use volts, amps and ohms (convert kΩ and mA first).
- Use P = V × I for power.
How to read your Ohm's Law result
Doubling the voltage across the same resistor doubles the current and quadruples the power.
Common mistakes when calculating Ohm's Law
- Mixing mA with A or kΩ with Ω.
- Applying Ohm's law to non-ohmic parts such as diodes.
- Forgetting the load's power rating.
Ohm's Law FAQ
What is Ohm's law?
It states that the current through a conductor is proportional to the voltage across it, V = I × R, at constant temperature.
How do I find power from voltage and current?
Multiply them: P = V × I, in watts.
Does Ohm's law work for AC?
For purely resistive loads, yes, using RMS values. Coils and capacitors need impedance instead of resistance.
What is the unit of resistance?
The ohm (Ω). One ohm lets 1 amp flow under 1 volt.
Method, review and disclaimer
Edited by: Hemant Kumar and Anjita Rai, founders of ToolsVault (SEO and content professional, not a licensed adviser). Method: this tool runs in your browser using the formula shown on this page; the numbers you enter are not sent to our servers.
Disclaimer: For learning and design checks. Follow electrical safety rules for real wiring.