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LED Resistor Calculator

Calculate the resistor needed to safely connect an LED to a power supply.

Basic LED Circuit
VCC
→
R
→
LED
→
GND
STEP 1

What do you want to calculate?

Resistor Value Calculate R
LED Current Calculate I
Supply Voltage Calculate Vs
LED Forward Voltage Calculate Vf
Result

What is an LED Resistor?

An LED resistor limits the current flowing through an LED. Without suitable current limiting, the LED can be damaged.

LED Resistor Formula

R = (Vs - Vf) ÷ I

Variables

  • Vs = Supply voltage
  • Vf = LED forward voltage
  • I = LED current
  • R = Series resistor

Example

Suppose you have a 5 V supply, a red LED with a forward voltage of 2 V, and you want 20 mA.

R = (5 - 2) ÷ 0.020

R = 150 Ω

Common LED Forward Voltages

  • Red LED: approximately 1.8 to 2.2 V
  • Yellow LED: approximately 2.0 to 2.2 V
  • Green LED: approximately 2.0 to 3.2 V
  • Blue LED: approximately 2.8 to 3.4 V
  • White LED: approximately 2.8 to 3.4 V

Resistor Power

The resistor also dissipates power. After calculating the resistor value, check its power rating.

P = I² × R