Ohm's Law Calculator
Enter any two of voltage, current, resistance and power to calculate the other two with Ohm's law and the power formula. Free electrical calculator.
Enter any two values; the other two are calculated.
- Resistance
- 6 Ω
- Power
- 24 W
V = I × R · P = V × I = I²R = V²/R
V = I × R
Ohm's law links voltage (V, in volts), current (I, in amps) and resistance (R, in ohms): V = I × R. Combined with the power formula P = V × I, any two of the four values give you the other two. A 12 V supply across a 6 Ω resistor drives 2 A and dissipates 24 W. Use it to size resistors for LEDs, check a fuse rating, or convert between watts and amps for an appliance.
How to use it
- 1
Enter two values
Any two of voltage, current, resistance and power.
- 2
Leave the others empty
They're calculated for you.
- 3
Read the results
All four values, with the formulas.
Frequently asked questions
How do I convert watts to amps?
Amps = watts ÷ volts. A 2,000 W kettle on 230 V draws about 8.7 A; on 120 V, about 16.7 A.
What resistor do I need for an LED?
R = (supply voltage − LED voltage) ÷ LED current. For 5 V, a 2 V LED and 20 mA: (5 − 2) ÷ 0.02 = 150 Ω.
Does Ohm's law work for AC?
For purely resistive loads, yes. Motors and electronics add reactance, so real current can differ.
Is anything sent to a server?
No. Everything is calculated in your browser, and nothing you type is stored or sent anywhere.