LED Resistor Calculator
Calculate the current-limiting resistor value for an LED circuit.
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Common LED Forward Voltages
| LED Color | Forward Voltage | Typical Current |
|---|---|---|
| Red | 1.8–2.2V | 20mA |
| Orange | 2.0–2.2V | 20mA |
| Yellow | 2.0–2.2V | 20mA |
| Green | 2.0–3.0V | 20mA |
| Blue | 3.0–3.4V | 20mA |
| White | 3.0–3.4V | 20mA |
| UV | 3.1–3.5V | 20mA |
| Infrared | 1.2–1.6V | 20–50mA |
How to Size an LED Resistor
LEDs require a current-limiting resistor to prevent them from burning out. Without one, an LED will draw excessive current and fail almost instantly.
The formula is simple: R = (Vsupply − Vled) / Iled. For multiple LEDs in series, subtract the total LED voltage drop: R = (Vsupply − N × Vled) / Iled.
Always choose a standard resistor value equal to or greater than the calculated value. A slightly higher resistance means slightly less current and brightness, which is always safer than too little resistance.
Check the power dissipation: P = (Vsupply − Vled) × Iled. Use a resistor rated for at least twice this power to ensure long life.