Ohm's Law Calculator
Enter any two of voltage (V), current (I), resistance (R) or power (P); the other two are calculated automatically.
Enter any two values.
Disclaimer: This calculator is provided for general informational and educational purposes only, on an “as is” basis and without any warranty of accuracy or fitness for a particular purpose. Results may contain errors — always verify independently before relying on them in real designs. PartAndStock accepts no liability for any loss or damage arising from use of this tool, including when embedded on third-party sites.
How to use
- 1Enter any two values you know (V, I, R or P).
- 2The other two values are calculated automatically.
- 3Copy the results or clear the inputs to start over.
How it works
Use Ohm's law (V = I × R) and power (P = V × I) to find the unknown values from any two known ones.
How the calculation works
Ohm's law is based on the fundamental relationship between voltage (V), current (I) and resistance (R) in a conductor: V = I × R. Combined with the power relations (P = V × I), any two of these four quantities let you calculate the other two — which is exactly what this calculator does.
Watch your units
To get the right answer, don't mix units: voltage in volts (V), current in amperes (A), resistance in ohms (Ω), power in watts (W). If you work in milliamps (mA), divide by 1000 to get amperes (e.g. 20 mA = 0.02 A); otherwise the result is off by a factor of 1000.
Worked examples
- 12 V and 0.5 A → R = 12 / 0.5 = 24 Ω, P = 12 × 0.5 = 6 W
- 12 V and 6 W → R = 12² / 6 = 24 Ω, I = 6 / 12 = 0.5 A
Ohm's Law Formulas
| To find | Formulas |
|---|---|
| Voltage (V) | V = I × R = P / I = √(P × R) |
| Current (I) | I = V / R = P / V = √(P / R) |
| Resistance (R) | R = V / I = V² / P = P / I² |
| Power (P) | P = V × I = I² × R = V² / R |