Ohm’s Law Calculator
Voltage, current, resistance and power from any two of them, all six combinations, by Ohm’s law and the power relationships.
Result
Current: 0.025532 A
For resistive circuits. With AC motors and electronics, power also depends on the power factor.
- Power
- 0.306383 W
- Voltage
- 12 V
- Resistance
- 470 Ω
https://calcgallery.com/electronics/ohms-law-calculator/
Results come from the published equations applied to the values you enter. They are not electrical design, conductor sizing, laboratory safety or medical guidance. Weather indices describe a standard person in standard conditions and are not a forecast. Where codes apply, local rules vary and must be checked. Read the full disclaimer
How to use the Ohm’s Law Calculator
- Choose which two of voltage, current, resistance and power you know.
- Enter those two, in whichever units suit, from millivolts to kilohms.
- Read the other two, with all four shown together.
The relationships
V = I × R I = V ÷ R R = V ÷ IP = V × I = I² × R = V² ÷ RFrom any two of the four quantities the other two follow, in six possible pairs. The page solves all six, and whichever pair you start from, the same circuit gives the same four values.
Units
Enter voltage in volts, millivolts or kilovolts, current in amperes or milliamperes, resistance in ohms, kilohms or megohms, and power in watts or kilowatts. Everything is converted to volts, amperes, ohms and watts before the calculation, and resistance is shown with the prefix that suits it.
What the diagram shows
The Ohm’s law triangle: voltage on top, current and resistance below. Cover the one you want, and the other two show how to get it: V over R for current, V over I for resistance, I beside R, multiplied, for voltage.
With your numbers
- V = I × R: 12 V = 0.025532 A × 470 Ω
- P = V × I = 0.306383 W
Quick reference
For resistive circuits. With AC motors and electronics, power also depends on the power factor.
| Example | Result |
|---|---|
| 12 V across 470 Ω | Current: 0.025532 A |
| 12 V at 2 A | Resistance: 6 Ω |
| 0.5 A through 100 Ω | Voltage: 50 V |
| 100 Ω dissipating 25 W | Current: 0.5 A |
| 1,500 W heater on 120 V | Current: 12.5 A |
| 2 A drawing 24 W | Voltage: 12 V |
| 12 V across 0 Ω | Current: |
Common questions about the Ohm’s Law Calculator
- What is Ohm's law?
- The voltage across a resistor equals the current through it times its resistance: V = I × R. Double the voltage across a fixed resistor and the current doubles. It holds for resistors and for many conductors at a steady temperature, though not for every component, such as diodes.
- How is power worked out?
- Power is voltage times current, P = V × I. Substituting Ohm's law gives two more forms, P = I² × R and P = V² ÷ R, which is how the page gets power from any pair. A 1,500 W heater on 120 V draws 12.5 A and has a resistance of 9.6 Ω while hot.
- What happens at zero resistance?
- A voltage across zero resistance would drive an unlimited current: a short circuit. In practice the wiring, the source's own resistance and fuses or breakers limit it. The page says so instead of printing infinity.
- Does this work for AC mains?
- For resistive loads such as heaters and incandescent lamps, yes, using RMS values. Motors, transformers and electronics also have reactance, and their real power is lower than volts times amps by the power factor, which this page does not model.