LED Resistor Calculator
Calculate LED current limiting resistor
LED color picker
Standard resistor values
Wattage rating
You want to connect an LED to your Arduino. The tutorial says "use a resistor" but doesn't specify which one. Too small and the LED burns out. Too large and it barely glows. What value actually works?
LED resistor calculation is the most common beginner electronics task—and the most commonly messed up. This calculator tells you exactly what resistor you need based on your supply voltage, LED specs, and desired brightness.
What is LED Resistor Calculation?
LEDs require current limiting resistors because LEDs are current-sensitive devices. Unlike incandescent bulbs, LEDs don't self-regulate—without a resistor, current increases until the LED destroys itself.
The formula:
R = (Vsupply - Vforward) / Iled
Where:
Vsupply = Power source voltage
Vforward = LED forward voltage (depends on color)
Iled = Desired LED current (typically 10-20mA)
Red/Yellow: ~2V. Green/Blue/White: ~3.2V. These are typical values—check your LED's datasheet for exact specs.
Why People Actually Need This Tool
A resistor self-limits current. An LED's resistance drops as it heats up, causing more current, more heat—thermal runaway until failure.
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Arduino/microcontroller projects — LED indicators, displays, signals.
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Automotive lighting — 12V systems require proper resistors.
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Hobby electronics — LED strips, custom lighting, decorations.
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Indicator circuits — Status LEDs in enclosures.
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Learning electronics — First practical circuit for beginners.
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Replacement LEDs — Match brightness of original circuit.
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Multiple LED circuits — Series and parallel configurations.
How to Use the LED Resistor Calculator
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Enter supply voltage — Your power source (5V, 12V, etc.).
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Enter LED forward voltage — From datasheet or color estimate.
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Enter desired current — Typically 10-20mA for indicator LEDs.
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Get resistor value — Plus nearest standard value and power rating.
| LED Color | Typical Vf | Typical Current | 5V Resistor | 12V Resistor |
|---|---|---|---|---|
| Red | 2.0V | 20mA | 150Ω | 500Ω |
| Yellow | 2.1V | 20mA | 145Ω | 495Ω |
| Green | 3.2V | 20mA | 90Ω | 440Ω |
| Blue | 3.3V | 20mA | 85Ω | 435Ω |
| White | 3.2V | 20mA | 90Ω | 440Ω |
A resistor dropping 10V at 20mA dissipates 0.2W. Use at least a 1/4W resistor—never push components to their limit.
Real-World Use Cases
1. The Arduino LED
Context: Connecting LED to Arduino 5V pin for indicator.
Problem: What resistor for a red LED at reasonable brightness?
Solution: R = (5V - 2V) / 0.015A = 200Ω. Use 220Ω standard value.
Outcome: LED glows nicely at ~14mA, well within Arduino pin current limit.
2. The 12V Automotive
Context: Adding blue LED indicator in car dashboard (12V system).
Problem: What resistor for 12V?
Solution: R = (12V - 3.3V) / 0.020A = 435Ω. Use 470Ω standard.
Outcome: LED operates safely in automotive environment.
3. The Battery Project
Context: 9V battery powering white LED.
Problem: What resistor, and how long will battery last?
Solution: R = (9V - 3.2V) / 0.020A = 290Ω. Use 330Ω. At 17mA, 9V battery (500mAh) lasts ~29 hours.
Outcome: Proper resistor and realistic battery life expectation.
4. The Dim Indicator
Context: Need subtle power indicator, not blindingly bright.
Problem: How to make LED dimmer?
Solution: Reduce current to 5mA. R = (5V - 2V) / 0.005A = 600Ω. Use 680Ω.
Outcome: Subtle glow that doesn't distract.
5. The Multiple LEDs in Series
Context: Three red LEDs in series from 12V.
Problem: What single resistor works?
Solution: Total Vf = 3 × 2V = 6V. R = (12V - 6V) / 0.020A = 300Ω.
Outcome: One resistor, three LEDs, proper current for all.
6. The Bright LED
Context: High-brightness LED rated for 30mA, needs maximum output.
Problem: Resistor for 30mA from 5V?
Solution: R = (5V - 3.2V) / 0.030A = 60Ω. Use 56Ω, running at ~32mA.
Outcome: LED at full brightness within safe operating range.
7. The Replacement Calculation
Context: Old circuit had LED with burned resistor. Need replacement.
Problem: Calculate correct value from remaining info.
Solution: Measure supply (12V), estimate LED Vf (red, ~2V), assume 20mA. R = 500Ω.
Outcome: Circuit restored with properly calculated component.
Common Mistakes and How to Avoid Them
An LED connected directly to 5V without a resistor will conduct excessive current and fail within seconds.
Privacy and Data Handling
This LED Resistor Calculator operates entirely in your browser.
- No calculations are sent to any server.
- No circuit designs are stored.
- No account required.
- Works completely offline.
Your projects stay private.
Conclusion
LED resistor calculation is fundamental to electronics. Getting it right means long-lasting, properly bright LEDs. Getting it wrong means burned-out components and frustration.
This calculator does the math correctly every time. Enter your voltage and LED specs, get the exact resistor value with standard value recommendation and power rating.
Light up your projects safely.