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LED Resistor Calculator

Calculate the correct resistor value for LED circuits. Free online calculator with instant results for supply voltage, forward voltage, and current with standard resistor recommendations.

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LED Resistor Calculator

Calculate the correct current-limiting resistor value for LED circuits. Prevents LED damage and ensures optimal brightness.

Actions

Circuit Parameters

V
V

💡 Depends on LED color (see presets below)

mA

Typical LED current: 10-20mA (standard), 20-30mA (high brightness)

Common LED Types

About LED Resistor Calculator

The LED Resistor Calculator helps you determine the correct current-limiting resistor value for LED circuits. LEDs require a resistor to prevent damage from excessive current. This free online tool calculates the exact resistor value, suggests standard resistor values, and recommends the appropriate power rating.

LED Resistor Formula

R = (Vs - Vf × N) / I

Where:

  • • R = Resistance in Ohms (Ω)
  • • Vs = Supply Voltage
  • • Vf = LED Forward Voltage
  • • N = Number of LEDs in series
  • • I = LED Current in Amperes

Common LED Forward Voltages

Red LED

Forward Voltage: 1.8-2.2V (typical 2.0V)

Green LED

Forward Voltage: 2.0-2.2V (typical 2.1V)

Yellow LED

Forward Voltage: 2.0-2.2V (typical 2.1V)

Blue/White LED

Forward Voltage: 3.0-3.4V (typical 3.2V)

How to Use This Calculator

  1. Enter Supply Voltage: The voltage source powering your circuit (e.g., 5V, 9V, 12V)
  2. Enter LED Forward Voltage: Check LED datasheet or use presets for common colors
  3. Enter LED Current: Typical values are 10-20mA for standard LEDs
  4. Set Number of LEDs: If connecting multiple LEDs in series
  5. View Results: Get exact and standard resistor values with power rating

Important Safety Notes

Always use a resistor: Never connect an LED directly to a power source without a current-limiting resistor.

Power rating: Use a resistor with at least 2× the calculated power dissipation for safety and longevity.

Check polarity: LEDs are polarized - connect the longer leg (anode) to positive and shorter leg (cathode) to negative.

Heat dissipation: If the resistor gets hot, use a higher wattage rating or reduce the current.

Example Calculations

Example 1: Red LED with 5V Supply

Supply: 5V | LED: 2.0V @ 20mA

Result: 150Ω resistor (0.25W)

Example 2: White LED with 9V Supply

Supply: 9V | LED: 3.2V @ 20mA

Result: 290Ω → 330Ω resistor (0.25W)

Example 3: Two Red LEDs in Series with 12V

Supply: 12V | 2× LEDs: 2.0V @ 20mA

Result: 400Ω → 390Ω resistor (0.25W)

Common Applications

  • ✓ Arduino Projects: Calculate resistors for LED indicators and displays
  • ✓ Raspberry Pi: Connect LEDs to GPIO pins safely
  • ✓ DIY Electronics: Build custom LED circuits and lighting projects
  • ✓ Automotive: Add LED indicators and accent lighting
  • ✓ Home Automation: Create LED status indicators for smart devices
  • ✓ Educational: Learn about Ohm's Law and LED circuits

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