Handyman Calculator

LED Resistor Calculator: Find the Right Resistor for Any LED (12V, 5V, 220V & More)

The LED Resistor Calculator calculates the resistor value required for LED circuits. Input source voltage, LED voltage, and LED current to determine the recommended resistor value and power rating. This calculator uses Ohm’s Law to provide accurate calculations for safe LED operation.

LED resistor calculator for 12V, 5V, and 220V circuits showing a single LED with a resistor and formula (R = (Vs - Vf) / If)

What Is an LED Resistor Calculator?

An LED resistor calculator is a tool that uses Ohm’s Law to determine the proper resistor value for LED circuits. It helps ensure that your LED receives the correct current by calculating the voltage drop across the resistor. This resistor LED calculator is essential for designing LED circuits that are safe and reliable.

How to Calculate the Right Resistor for an LED

For any LED circuit, a current-limiting resistor is critical to prevent burnout. Here’s how our calculator works:
Key Formula

Using Ohm’s Law, the resistor value is calculated as:

The calculator follows these steps:

Where:

  • =Power supply voltage (e.g., 5V, 12V, 220V).
  • =LED forward voltage (typically 2-3.5V).
  • =LED current in milliamps (mA).

Examples: LED Resistor Calculation

Example 1: 5V Circuit (Common for Arduino)

  • Input Values:
    • Source Voltage (​): 5V
    • LED Voltage (​): 2.2V (standard red LED)
    • LED Current (​): 20mA

Step 1: Voltage Drop

Step 2: Resistor Value

Step 3: Power Dissipation

Result: Use a 150Ω resistor (closest standard value) with a 0.125W (1/8W) rating.

Example 2: 12V Automotive Lighting

  • Input Values:
    • Source Voltage: 12V
    • LED Voltage: 3.4V (white LED)
    • LED Current: 30mA

Resistor Value:

Result: Use a 270Ω or 330Ω resistor.

Example 3: 220V Mains Voltage (Caution!)

  • Input Values:
    • Source Voltage: 220V
    • LED Voltage: 3V
    • LED Current: 20mA

Resistor Value:

Power Dissipation:

Result: A 10kΩ, 5W resistor is required. Always use additional circuitry (e.g., capacitor dropper) for AC/220V applications.

Depending on your circuit configuration, you might need to use our Series LED Resistor Calculator or Parallel LED Resistor Calculator for more specific resistor calculations.

FAQs

Is a 1K Resistor Too Much for an LED?

A 1K resistor (1,000Ω) is generally safe for most LEDs and simplifies circuit design. LEDs are less sensitive to current variations than bulbs, so brightness remains stable even with resistor value changes. If the LED seems too bright with a 1K resistor, you can try higher values like 2K ohms or more to reduce the brightness.

LED Resistor Calculator

Calculate the required resistor value and power rating for your LED circuit. Make sure to use a resistor with a power rating higher than the calculated value.