LED Resistor Calculator | LED Current Limiting Resistor

📖 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)

Where:
Vs = Supply Voltage (V) Vf = LED Forward Voltage (V)
I = LED Current (A) N = Number of LEDs
R = Resistor Value (Ω) P = Power (W)

📊 Common LED Specifications

LED Color	Forward Voltage (Vf)	Typical Current (mA)	Wavelength
Red	1.8 - 2.2	20	620-660nm
Green	2.0 - 2.4	20	520-560nm
Yellow	2.0 - 2.2	20	580-590nm
Orange	2.0 - 2.2	20	590-610nm
Blue	3.0 - 3.4	20	460-490nm
White	3.0 - 3.6	20	450-470nm
IR (Infrared)	1.2 - 1.5	20-50	850-940nm
UV (Ultraviolet)	3.2 - 4.0	20	365-405nm

📌 Standard Resistor Values (E12 series)

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 (FAQ)

❓ How to calculate resistor for LED? ▼

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

❓ What resistor for 5V LED? ▼

For a 2V LED at 20mA with 5V supply, R = (5-2)/0.02 = 150Ω. For 3.2V LED, R = (5-3.2)/0.02 = 90Ω → use 100Ω.

❓ What is LED forward voltage? ▼

Forward voltage (Vf) is the voltage drop across the LED when conducting. 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. Use this calculator for both configurations.

❓ What is the resistor power rating? ▼

Power = I² × R. For 20mA through 150Ω, P = (0.02)² × 150 = 0.06W. Use 0.25W (1/4W) resistor for safety.

❓ Can I connect LED without resistor? ▼

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