Electronics & Engineering

Ohm's Law Calculator

Pick the two values you know and get the other two.

By TheCalcTools Updated Formula checked and tested

Your numbers

Your results

Voltage (V)
Voltage (V)
—
Current (A)
—
Resistance (Ω)
—
Power (W)
—

Ohm's Law Calculator by TheCalcTools

How the Ohm's Law Calculator works

Choose which pair of values you know, then enter them in the order shown: voltage and current, voltage and resistance, or current and resistance.

Ohm’s law links the three: V = I × R.

Power is voltage times current.

The formula

V = I × RI = V ÷ R

Worked example

Using the default values shown in the calculator:

I knowVoltage and current
First value (V, V or A)12
Second value (A, Ω or Ω)3
  1. Known: 12 V and 3 A.
  2. R = 12 ÷ 3 = 4.00 Ω.
  3. P = 12 × 3 = 36.00 W.

Result:

Voltage (V)12.0000
Current (A)3.0000
Resistance (Ω)4.0000
Power (W)36.0000

Frequently asked questions

Does Ohm's law apply to every component?

No. It describes ohmic materials such as resistors, where resistance is constant. Diodes and transistors do not follow it.

How do I find the power from current and resistance?

P = I² × R. The calculator uses P = V × I, which gives the same answer.

Sources and further reading

Electrical Power Calculator (Single and Three Phase)Work out watts, kVA and kvar from volts, amps and power factor Voltage Divider CalculatorFind the output of a resistor divider from the input voltage and R1 and R2 Resistors in Series and Parallel CalculatorCombine up to four resistors Capacitors in Series and Parallel CalculatorCombine up to four capacitors LED Resistor CalculatorPick a resistor that sets the right current through an LED Resistor Color Code CalculatorChoose the colours of the four bands to read the value

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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.