LED Resistor Calculator
Calculate the required current-limiting resistor for a single LED, or for multiple LEDs in series or parallel. This calculator helps you select the correct resistor to safely power your LEDs without damaging them.
LED Circuit Parameters
How to Calculate the LED Resistor
To prevent an LED from burning out, a current-limiting resistor is used. The value of this resistor is calculated using Ohm's Law.
Formula for a Single LED or Series Circuit
- R = Resistor value in Ohms (Ω)
- Vs = Source Voltage in Volts (V)
- Vf = LED Forward Voltage in Volts (V)
- n = Number of LEDs in series
- If = LED Forward Current in Amperes (A)
Formula for Parallel Circuits
For parallel circuits, you calculate the resistor for each LED string. If all LEDs are the same, you only need to do one calculation.
The total current drawn from the source will be the sum of the currents of all parallel branches.
Common LED Forward Voltages (Vf)
| LED Color | Forward Voltage (Vf) | Forward Current (If) |
|---|---|---|
| Red | 1.8V - 2.2V | 20mA |
| Green | 2.0V - 3.4V | 20mA |
| Blue | 3.2V - 3.4V | 20mA |
| White | 3.2V - 3.4V | 20mA |
| Yellow | 2.0V - 2.2V | 20mA |
| Infrared (IR) | 1.2V - 1.5V | 20mA - 50mA |
Frequently Asked Questions
Why do I need a resistor for an LED?
LEDs have very little internal resistance. Without a current-limiting resistor, they would draw too much current from the power source, causing them to burn out almost instantly. The resistor ensures the current stays at a safe level.
What happens if I use the wrong resistor?
If the resistor value is too low, too much current will flow, and the LED will likely be destroyed. If the resistor value is too high, the LED will be dimmer than intended, or may not light up at all.
What does 'forward voltage' mean?
Forward voltage (Vf) is the amount of voltage required to make the LED light up. This value varies depending on the color and type of the LED.