LED Resistor Calculator
Current-limiting resistor value for an LED circuit.
Enter your values
ⓘ Live results
Results
- Resistor value
- 350 Ω
- Resistor power rating
- 0.28 W (2x safety margin)
- Actual power dissipated
- 0.14 W
Quick answer
Resistor R = (supply voltage - LED forward voltage) / desired current.
R = (Vs - Vf) / I
How to use the LED Resistor Calculator
- 1Enter your supply voltage and the LED's forward voltage (check the datasheet, typically 1.8-3.3V).
- 2Enter the desired LED current, commonly 20mA for standard indicator LEDs.
- 3Round up to the nearest standard resistor value and pick a power rating with margin.
Worked example
Using the values the calculator loads with:
Inputs
- Supply voltage9 V
- LED forward voltage2 V
- Desired LED current20 mA
Results
- Resistor value350 Ω
- Resistor power rating0.28 W (2x safety margin)
- Actual power dissipated0.14 W
Frequently asked questions
What if I use the wrong resistor value?
Too low burns out the LED quickly; too high makes it dim or fail to light.
Why double the power rating?
It keeps the resistor running cool, extending its life and improving reliability.
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.