Ohm’s law calculator
Fill in any two of V, I, R and P; the other two are calculated.
Resistance
Resistance: 6 Ω
- Voltage
- 12 V
- Current
- 2 A
- Power
- 24 W
How it works
Ohm’s law says the current through a resistor is the voltage across it divided by its resistance. The power it uses is voltage times current.
Combining the two gives a formula for every pair: for example P = I²R or I = √(P ÷ R). Use volts, amps, ohms and watts; for milliamps, divide by 1000 first.
Formula
V = I × R P = V × I P = I² × R = V² ÷ R I = √(P ÷ R)
Worked example
A 12 V supply driving 2 A means R = 12 ÷ 2 = 6 Ω and P = 12 × 2 = 24 W.
Questions people ask
Does Ohm’s law work for every component?
It holds for ordinary resistors at steady temperature. LEDs, diodes and lamps are non-linear, so their resistance changes with the current.
How much current does a 2000 W kettle draw at 230 V?
I = P ÷ V = 2000 ÷ 230 ≈ 8.7 A.
Is this for AC or DC?
DC, or AC with purely resistive loads using RMS values. Circuits with capacitors or motors need impedance and power factor.