About the Ohm's Law Calculator
Ohm's law is the single most useful relationship in electronics: V = I × R. Combined with P = V × I it forms the power wheel, so any two of voltage, current, resistance and power determine the other two. Enter the two you know and this calculator fills in the rest.
Also known as: v=ir calculator, ohms law, volts amps ohms, power wheel, ohm law formula, watts volts amps calculator.
How to use this calculator
- Pick the pair of values you already know.
- Enter them — the rest of the circuit values are calculated instantly.
- Use the power figure to size fuses, wires and heat sinks.
Formula
V = I × R · P = V × I = I²R = V²/R
- V
- = voltage in volts
- I
- = current in amperes
- R
- = resistance in ohms
- P
- = power in watts
Worked example
Using the values pre-filled in the calculator above:
- I know: Voltage and current
- Voltage = 12 V
- Current = 2 A
the calculator returns:
- Voltage: 12 V
- Current: 2 A
- Resistance: 6 Ω
- Power: 24 W
Working
V = I × R = 2 × 6 = 12 VP = V × I = 12 × 2 = 24 W
Tips & common mistakes
- Halving the resistance doubles the current at a fixed voltage.
- Power rises with the square of current, so a small current increase heats a resistor a lot.