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๐Ÿ’ก LED Resistor Calculator

Calculate the correct current-limiting series resistor for your LED circuit. Get instant results with power dissipation and nearest standard resistor values.

๐Ÿ”ง Calculate LED Resistor

The voltage of your power supply (Arduino: 5V, ESP32: 3.3V)
Select LED color to auto-fill typical forward voltage
Standard LEDs: 10-20mA, High-brightness: 20-30mA

๐Ÿ“ The LED Resistor Formula

R = (Vs - Vf) / I
Where R = Resistance (ฮฉ), Vs = Source Voltage, Vf = Forward Voltage, I = Current (A)

This formula comes from Ohm's Law. The resistor must drop the difference between your power supply voltage and the LED's forward voltage. The current through the resistor equals the current through the LED (they're in series).

Step-by-Step Example

Let's calculate the resistor needed for a red LED powered by an Arduino (5V):

  1. Source Voltage (Vs): 5V (Arduino output)
  2. LED Forward Voltage (Vf): 2.0V (typical for red LED)
  3. Desired Current (I): 20mA = 0.020A
  4. Calculate: R = (5 - 2) / 0.020 = 150ฮฉ

Result: Use a 150ฮฉ resistor (or next standard value: 180ฮฉ for safety margin).

๐ŸŒˆ LED Forward Voltage Reference

Different LED colors have different forward voltage drops. Use this table as a quick reference:

LED Color Forward Voltage (Vf) Typical Current
Red 1.8V - 2.2V 20mA
Orange 2.0V - 2.2V 20mA
Yellow 2.0V - 2.4V 20mA
Green 2.0V - 3.0V 20mA
Blue 3.0V - 3.5V 20mA
White 3.0V - 3.5V 20mA
RGB (each channel) 2.0V - 3.3V 20mA per channel
UV/Purple 3.2V - 4.0V 20mA
Infrared (IR) 1.2V - 1.6V 50-100mA

Note: Always check your LED's datasheet for exact specifications. Values can vary between manufacturers.

โš ๏ธ Why Do LEDs Need a Resistor?

LEDs are current-controlled devices, not voltage-controlled. Without a current-limiting resistor, an LED will try to draw as much current as possible, leading to:

  • Instant burnout: The LED will overheat and fail within seconds
  • Damage to your microcontroller: GPIO pins have current limits (typically 20-40mA)
  • Reduced lifespan: Even if it survives, running at excessive current drastically reduces LED life

What Happens Inside the Circuit

When you power an LED:

  1. The LED maintains a relatively constant voltage drop (the forward voltage)
  2. The resistor drops the remaining voltage
  3. Ohm's Law (V = IR) determines how much current flows
  4. The resistor "limits" the current to a safe value

โ“ Frequently Asked Questions

Can I use a higher resistance value than calculated?

Yes! A higher resistance will result in lower current and a dimmer LED, but it won't damage anything. This is a common way to dim LEDs without PWM.

What happens if I use a lower resistance value?

Lower resistance means higher current. If you exceed the LED's rated current, it will run hot and may burn out. Your GPIO pin could also be damaged if it exceeds its current limit.

What wattage resistor should I use?

Calculate power dissipation: P = Iยฒ ร— R. For most LED circuits (20mA with 150ฮฉ = 0.06W), a standard 1/4W (0.25W) resistor is more than sufficient. Our calculator shows the recommended wattage.

Can I connect multiple LEDs to one resistor?

Yes, but the calculation changes. LEDs in series: Add up all the forward voltages, then calculate R = (Vs - (Vf1 + Vf2 + ...)) / I. LEDs in parallel: Each LED needs its own resistor for even current distribution.

Why doesn't my calculated value match a standard resistor?

Resistors come in standard series (E12, E24, E96). Our calculator shows the nearest standard value. Always choose the next higher standard value for safety.