This Ohm’s law calculator finds voltage, current, resistance and power. Enter any two values and leave the other two empty.
Ohm’s law and power formulas
V = I × R and P = V × I
Combining them gives P = I²R and P = V² ÷ R, so any two values are enough to find the rest.
Worked example
A 12 V battery connected to a 6 Ω resistor drives a current of 12 ÷ 6 = 2 A, and the resistor uses 12 × 2 = 24 W of power.
Frequently asked questions
Does Ohm’s law apply to everything?
It applies to resistors and many conductors at a steady temperature. Components such as diodes, LEDs and bulbs whose resistance changes with temperature do not follow it exactly.
Why does power matter?
A resistor must be rated for at least the power it will dissipate, or it can overheat. Choosing one rated about double the calculated power is a common safety margin.