Ohm's law calculator
Enter two quantities and we calculate the third from U = I × R – together with the power P.
Calculate
Current I: 2.3 A
Real power P: 529 W
How the calculator works
Ohm's law describes the relationship between voltage, current and resistance: U = I × R. Pick the quantity you want to calculate, enter the other two, and the result appears instantly – including the power P = U × I, which is calculated automatically.
Example: a 100 Ω resistor connected to 230 V passes a current of I = 230 / 100 = 2.3 A and dissipates 529 W. Ohm's law holds exactly for linear (ohmic) conductors – in bulbs or semiconductors the resistance changes with temperature, so treat the result as valid for that operating point.
Worked examples
| Input | Result |
|---|---|
| U = 230 V, R = 100 Ω | I = 2.3 A; P = 529 W |
| U = 12 V, I = 0.5 A | R = 24 Ω; P = 6 W |
| I = 16 A, R = 14.4 Ω | U = 230.4 V; P ≈ 3,686 W |
| U = 5 V, R = 220 Ω | I ≈ 22.7 mA; P ≈ 0.114 W |
Frequently asked questions
What does Ohm's law say?
The current through a conductor is directly proportional to the voltage and inversely proportional to the resistance: I = U / R. The forms U = I × R and R = U / I follow from it.
How do I calculate resistance from voltage and current?
R = U / I. For example, an appliance drawing 2 A at 230 V has a resistance of 115 Ω.
How does power relate to Ohm's law?
Power P = U × I can be rewritten via Ohm's law as P = I² × R or P = U² / R. The calculator adds it automatically to every result.
Does Ohm's law always hold?
It holds exactly for linear conductors with constant resistance (resistors, metal wires at constant temperature). In bulbs, diodes or thermistors the resistance changes with temperature or voltage.
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Last updated: 16 July 2026