LED Resistor Formula
R = (Vs - Vf) / I
| LED Color | Forward Voltage | Typical Current |
|---|---|---|
| Red | 1.7-2.0V | 20 mA |
| Yellow | 1.9-2.2V | 20 mA |
| Green | 2.0-3.0V | 20 mA |
| Blue | 3.0-3.5V | 20 mA |
| White | 3.0-3.5V | 20 mA |
LED Resistor Calculator
Calculate the correct resistor value for an LED circuit based on supply voltage, LED forward voltage, and current.
π How We Calculate — Learn about our calculation methodology, data sources, and quality standards.
Frequently Asked Questions
Why do LEDs need resistors?
LEDs have very low internal resistance. Without a current-limiting resistor, current surges through the LED causing it to burn out instantly.
Can I put multiple LEDs in series?
Yes, as long as total forward voltage is less than the supply voltage. For 3 white LEDs (3.3V each) you need at least 10V supply.
How to Use This LED Resistor Calculator
Enter the supply voltage, LED forward voltage, LED forward current, and number of LEDs. The calculator determines the required resistor value and power rating.
Formula & How It Works
R = (V_supply β V_LED) / I_LED. For series LEDs: R = (V_supply β n Γ V_LED) / I_LED. Power rating: P = IΒ² Γ R (choose a resistor rated β₯ 2Γ calculated power).
Calculation Example
A red LED (2V, 20mA) powered by 5V: R = (5 β 2) / 0.020 = 150Ξ©. Power = 0.02Β² Γ 150 = 0.06W β use a 1/4W resistor.
Expert Tips
Standard LED forward voltages: Red ~2V, Green ~2.2V, Blue/White ~3.2V. Always use a resistor β connecting an LED directly to power will burn it out instantly. Use the next higher standard resistor value.