Ohm’s Law & Power Calculator
Enter any two of voltage, current, resistance and power to find the other two, using V = IR and P = VI with SI prefixes like 4.7k and 20m.
Runs on your device
Result
Results appear here as you type.
What it does
The four quantities are tied together by V = I·R and P = V·I. Fill in any two and the calculator solves for the rest and shows which formulas it used.
How to use it
- Enter exactly two known values (leave the others blank).
- Use prefixes such as 4.7k Ω or 20m A.
- Read the computed values.
Example
12 V across 470 Ω draws 25.5 mA and dissipates 306 mW. Select Try an example above to see it.
When it helps
- Sizing resistors in lab circuits.
- Checking power ratings.
- Quick circuit sanity checks.
Questions
Why must I enter exactly two values?
Two independent values determine the other two. A third value could contradict them.
How do I enter milliamps?
Type 20m in the current field for 20 mA.
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