LED Resistor Calculator
Calculate the correct current-limiting resistor for LED circuits
Volts (V)
Volts (V) - typically 1.8-3.6V depending on LED color
Milliamperes (mA) - typically 10-30 mA for standard LEDs
Number of LEDs connected in series
How to Use This Calculator
Enter Supply Voltage
Enter the power supply voltage in volts (e.g., 5V for USB, 12V for car battery, 9V for battery).
Enter LED Specifications
Enter the LED forward voltage (typically 2-3.6V) and desired current (typically 10-30 mA). Check your LED datasheet for exact values.
Enter Number of LEDs
If connecting multiple LEDs in series, enter the number. Each LED will have the same current flowing through it.
Get Results
Click calculate to see the required resistor value and power rating. Always use a resistor rated for at least twice the calculated power.
Formula
R = (Vs - Vf × n) / I
P = I² × R
Where:
- R = Resistor value (Ω)
- Vs = Supply voltage (V)
- Vf = LED forward voltage (V)
- n = Number of LEDs in series
- I = LED current (A)
- P = Power dissipation (W)
Example 1:
Supply = 5 V, LED Vf = 2.0 V, Current = 20 mA, 1 LED
R = (5 - 2.0 × 1) / 0.02 = 3 / 0.02 = 150 Ω
P = 0.02² × 150 = 0.06 W (use 1/4 W resistor)
Example 2:
Supply = 12 V, LED Vf = 3.0 V, Current = 20 mA, 3 LEDs
R = (12 - 3.0 × 3) / 0.02 = 3 / 0.02 = 150 Ω
About LED Resistor Calculator
The LED Resistor Calculator helps you determine the correct current-limiting resistor for LED circuits. LEDs require a specific current to operate properly and safely. Without a current-limiting resistor, LEDs can be damaged by excessive current. This calculator determines the resistor value needed to limit current to the desired level.
When to Use This Calculator
- LED Circuit Design: Design LED circuits with proper current limiting
- Arduino Projects: Calculate resistors for Arduino LED projects
- LED Strips: Determine resistors for LED arrays
- Educational Purposes: Learn about LED circuit design
Why Use Our Calculator?
- ✅ Accurate Calculations: Uses correct LED resistor formula
- ✅ Multiple LEDs: Handles series-connected LEDs
- ✅ Power Rating: Calculates required resistor power rating
- ✅ Easy to Use: Simple interface
- ✅ Free Tool: No registration required
Common Applications
Indicator Lights: LEDs are commonly used as status indicators. A 5V supply with a 2V LED at 20mA requires a 150Ω resistor to limit current properly.
Arduino Projects: Arduino boards output 5V, and most LEDs need current limiting. This calculator helps select the right resistor for Arduino pin connections.
Tips for Accurate Results
- Check LED datasheet for exact forward voltage and maximum current
- Typical forward voltages: Red/Orange/Yellow = 2.0V, Green/Blue/White = 3.0-3.6V
- Standard LED current: 10-30 mA (20 mA is common)
- Always use resistor rated for at least 2× calculated power
- Round up to next standard resistor value
- For parallel LEDs, calculate resistor for each LED separately
Frequently Asked Questions
Why do LEDs need a resistor?
LEDs have very low resistance and will draw excessive current if connected directly to a voltage source, causing damage. A current-limiting resistor ensures the LED receives the correct current.
What happens if I use the wrong resistor?
Too small a resistor allows too much current, which can damage or destroy the LED. Too large a resistor reduces current too much, making the LED dim or not light at all.
Can I connect multiple LEDs to one resistor?
You can connect LEDs in series (one resistor for the chain) or in parallel (one resistor per LED). For series, add forward voltages. For parallel, calculate each LED separately.
What resistor power rating should I use?
Use a resistor rated for at least twice the calculated power dissipation. Common ratings are 1/4W, 1/2W, and 1W. For most LED circuits, 1/4W is sufficient.