LED Resistor Calculator | LED Current Limiting Resistor

🔌 Supply Voltage (V)

💡 LED Forward Voltage (V)

⚡ LED Current (mA)

🔢 Number of LEDs

🔗 LED Connection

💡 Formula: R = (V_supply - V_forward) / I_LED | Power = I² × R

R = (Vs - Vf) / I | P = I² × R

📖 LED Resistor Calculator

This tool calculates the current limiting resistor value needed for LEDs. When connecting an LED to a power supply, a resistor is required to limit the current and prevent the LED from burning out. Enter the supply voltage, LED forward voltage, and desired current to get the correct resistor value and power rating.

📐 LED Resistor Formulas

Series LEDs: R = (Vs - (Vf × N)) / I
Parallel LEDs: R = (Vs - Vf) / (I × N)
Power Rating: P = I² × R (use 2× for safety)

📊 Common LED Specifications

LED Color	Forward Voltage (Vf)	Typical Current (mA)
Red	1.8 - 2.2	20
Green	2.0 - 2.4	20
Yellow	2.0 - 2.2	20
Blue	3.0 - 3.4	20
White	3.0 - 3.6	20
IR (Infrared)	1.2 - 1.5	20-50
UV (Ultraviolet)	3.2 - 4.0	20

LED Color

Forward Voltage (Vf)

Typical Current (mA)

Red

1.8 - 2.2

Green

2.0 - 2.4

Yellow

2.0 - 2.2

Blue

3.0 - 3.4

White

3.0 - 3.6

IR (Infrared)

1.2 - 1.5

20-50

UV (Ultraviolet)

3.2 - 4.0

📌 Standard Resistor Values

Common values: 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82, 100Ω, 120, 150, 180, 220, 270, 330, 390, 470, 560, 680, 820Ω, 1kΩ, 1.2k, 1.5k, 1.8k, 2.2k, 2.7k, 3.3k, 3.9k, 4.7k, 5.6k, 6.8k, 8.2k, 10kΩ

💡 Tips for LED Circuits

Always use a resistor: Never connect an LED directly to a voltage source

Check polarity: LED anode (+) goes to positive, cathode (-) to negative

Power rating: Use resistor with 2× calculated power for safety

Series vs Parallel: Series uses less current but requires higher voltage

Brightness: Lower current = dimmer LED, longer life

❓ Frequently Asked Questions

❓ How to calculate resistor for LED? ▼

R = (Vs - Vf) / I. For example, 5V supply, 2V LED, 20mA current → R = (5-2)/0.02 = 150Ω.

❓ What resistor for 5V LED? ▼

For a 2V LED at 20mA with 5V supply, R = 150Ω. For 3.2V LED, R = 90Ω → use 100Ω.

❓ What is LED forward voltage? ▼

Forward voltage (Vf) is the voltage drop across the LED. Different colors have different Vf: red (~2V), blue/white (~3.2V).

❓ Series vs parallel LED connection? ▼

Series: same current through all LEDs, higher voltage required. Parallel: same voltage, current adds up.

❓ Can I connect LED without resistor? ▼

No! Without a current limiting resistor, the LED will draw excessive current and burn out instantly.