Ohm's Law Calculator (V, I, R, Power)
Calculate voltage, current, resistance, and electrical power from any 2 known values. Includes formulas, unit prefixes, and worked examples.
How it works
Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage across the two points. The standard formula is V = I × R.
Joule's Law relates power to voltage and current with the formula P = V × I.
By combining these two laws, you can find any two of the four variables (Voltage, Current, Resistance, Power) as long as the other two are known.
Worked example
If you have a 5V power supply and an LED circuit that requires 20mA (0.02A) of current, what is the total resistance of the circuit?
Using R = V / I, we get R = 5V / 0.02A = 250 Ω.
Frequently Asked Questions
Can I enter values in engineering notation like '4.7k'?
Yes! You can use standard suffixes like m, k, M, u, n, and p in any field.
What happens if I enter three values?
The calculator only requires two inputs to solve the equation. If you enter more, clear at least one to ensure the calculation is correct.
Sources
- Ohm, G.S. (1827). Die galvanische Kette, mathematisch bearbeitet.
- Standard electronics textbook formulas (e.g., The Art of Electronics).
Results are for engineering assistance. Verify important calculations and check official datasheets. See the Engineering Disclaimer.