Ohm's Law & Power Calculator
One calculator for watts, volts, amps, and ohms. Enter any two known values and instantly solve for the other two, using Ohm's Law (V = I × R) and Joule's Law (P = V × I).
Ohm’s Law: V = I × R · Power: P = V × I. Every result below is derived from these two relationships.
24 Ω
600 W
Watts, volts, amps and ohms — one relationship
Voltage, current, resistance, and power are all tied together by two rules: Ohm’s Law (V = I × R) and Joule’s Law (P = V × I). Because they share variables, any two known values are enough to derive the other two. That is why a “watts calculator”, a “voltage calculator”, an “amp calculator”, and a “power calculator” are really the same tool viewed from different angles — this page solves for all of them at once.
The 12 Ohm’s Law formulas
Every value can be found three different ways, depending on which two you already know.
Power (P)
- P = V × I
- P = I² × R
- P = V² ÷ R
Voltage (V)
- V = I × R
- V = P ÷ I
- V = √(P × R)
Current (I)
- I = V ÷ R
- I = P ÷ V
- I = √(P ÷ R)
Resistance (R)
- R = V ÷ I
- R = V² ÷ P
- R = P ÷ I²
Frequently asked questions
Ohm’s Law states that voltage equals current times resistance: V = I × R. Rearranged, current is I = V ÷ R and resistance is R = V ÷ I. It is the single most useful relationship in basic electronics and lets you find any one of the three values when you know the other two.
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