Formula
Resistance = (supply voltage − total LED forward voltage) ÷ current. Power = current² × resistance.
ELECTRONICS
LED Resistor Calculator
Estimate a current-limiting resistor and minimum power rating.
CALCULATOR GUIDE
How to use the LED Resistor Calculator
Find a series resistor for one or more LEDs using supply voltage, forward voltage and target current.
Worked example
A 9 V supply with one 2 V LED at 20 mA requires 350 Ω; selecting the next higher standard value reduces current slightly.
Assumptions and limits
Forward voltage varies with LED colour, temperature and part. Never exceed the datasheet current rating.
Frequently asked questions
Should I round the resistor up or down?
Choose the next higher standard value to keep LED current at or below the target.
Can multiple LEDs share one resistor?
Series LEDs may share a resistor when voltage allows; parallel branches should normally have separate resistors.
How this calculator works
Enter your known values and select Calculate result. Review units and inputs before relying on the planning estimate.
Actual quantities, prices and requirements can vary. Confirm critical work with a supplier or qualified professional.