LED Resistor Calculator
Series resistor for any LED.
Enter your values
ⓘ Live results
Results
- Resistor value
- 495 Ω
- Nearest E12 value
- 500 Ω
- Power dissipated
- 0.198 W
- Rating needed
- 0.25 W
Quick answer
The series resistor drops the difference between supply voltage and LED forward voltage.
R = (Vsupply − Vf) ÷ I
How to use the LED Resistor Calculator
- 1Enter the supply voltage.
- 2Enter LED forward voltage and desired current.
- 3Choose the next standard resistor above the result.
Worked example
Using the values the calculator loads with:
Inputs
- Supply voltage12 V
- LED forward voltage2.1 V
- LED current20 mA
- LEDs in series1
Results
- Resistor value495 Ω
- Nearest E12 value500 Ω
- Power dissipated0.198 W
- Rating needed0.25 W
Frequently asked questions
What is typical Vf?
About 2 V for red, 3.2 V for blue and white.
Can I skip the resistor?
No — LEDs have no internal current limiting and will burn out.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.