LED Resistor Calculator

Quickly calculate the required series resistor for your LED. Find the nearest standard resistor value and power dissipation to safely light up your project.

⚙️ Parameters

Source Voltage (V_S)

LED Color (Preset)

LED Forward Voltage (V_F)

This is the voltage drop across the LED.

LED Current (I_F) (mA)

Typically 15-20mA for standard 5mm LEDs.

📊 Results

Required Resistor:

Nearest Standard Resistor (E24):

Power Dissipation:

⚡ Circuit Diagram

Theory & Formulas

To prevent an LED from burning out, a series resistor is needed to limit the current flowing through it. The calculation is a direct application of Ohm's Law.

Ohm's Law for LEDs

The resistor's value is determined by the source voltage (V_S), the LED's forward voltage (V_F), and the desired forward current (I_F).

R = (V_S - V_F) / I_F

Where I_F is in Amperes (so we divide the milliamp value by 1000).

Power Dissipation

It's also crucial to use a resistor with an adequate power rating. The power dissipated by the resistor is calculated using the formula:

P = I_F² * R

If the power is over 0.25W, you should consider a resistor with a higher power rating (e.g., 1/2W or 1W).