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Ohm's Law Calculator

Calculate voltage, current, resistance and power. Free, fast and easy to use.

Calculator

Enter any two values and leave the third empty — it will be calculated.

Result 20 VVoltage
Current
2 A
Resistance
10 Ω
Power
40 W

How it works

Ohm's law links voltage (V), current (I) and resistance (R): V = I × R. Enter any two of the three values and the calculator finds the third, together with the power dissipated.

Formula

V = I × R    I = V / R    R = V / I
P = V × I

Worked examples

  • Voltage (V): 12 · Resistance (Ω): 220 → Voltage: 12 V
  • Voltage (V): 230 · Current (A): 10 → Voltage: 230 V
  • Current (A): 0.02 · Resistance (Ω): 500 → Voltage: 10 V

Calculations run locally in your browser. Results are for information only — for engineering, electrical or financial decisions, verify the assumptions and applicable standards.

Frequently asked questions

What is Ohm's law?

Voltage equals current times resistance: V = I × R. Rearranged, I = V / R and R = V / I.

What resistor do I need for an LED?

R = (supply voltage − LED voltage) / current. For 12 V, a 2 V LED and 20 mA: (12 − 2) / 0.02 = 500 Ω, so use the next standard value, 510 Ω.

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