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How to use
Use this Ohm’s law calculator to solve voltage V, current I, resistance R and electrical power P from any two known values. It combines V=IR with P=VI, P=I²R and P=V²/R, and supports common mA, µA, kΩ, MΩ and power prefixes.
- Fill exactly two fields and leave the other two blank.
- Choose the unit for each known value, such as mA or kΩ.
- Calculate to display V, I, R and P together in base SI units.
How it is calculated
Example
Example: 12 V and 4 Ω produce I=3 A and P=36 W. Using 500 mA and 24 Ω produces 12 V and 6 W after the calculator normalizes 500 mA to 0.5 A.
Important notes
The model assumes an ideal ohmic element using non-negative magnitudes in DC or a purely resistive case. In reactive AC circuits or when power factor is not 1, resistance becomes impedance and P=VI is not generally real power. Underdetermined zero pairs such as V=0 and I=0 are rejected rather than inventing a resistance.
Worked examples and interpreting results
With a voltage of 12 volts and a current of 2 amperes, Ohm's law gives resistance of 6 ohms and power of 24 watts.
| Case | Calculation | Result |
|---|---|---|
| Resistance R | 12 V ÷ 2 A | 6 Ω |
| Electrical power P | 12 V × 2 A | 24 W |
How to check the result
Enter exactly two of voltage, current, resistance and power. This ideal resistive model does not address electrical installation safety or all AC circuit behavior.
Frequently asked questions
What is Ohm’s law?
Ohm’s law is V=IR: voltage equals current multiplied by resistance. Rearranging gives I=V/R and R=V/I.
Do I need to convert mA to A manually?
No. Select mA and the calculator normalizes it internally.
Can I enter resistance and power only?
Yes. For an ideal resistor it solves I = √(P/R) and then V = IR.
Does this work for motors and general AC circuits?
Not by itself. Reactive AC cases may require impedance, phase and power factor.