LED Resistor Calculator
Calculate the current-limiting resistor for single or multiple LEDs in series or parallel.
Free & unlimitedWorks offline
LED type
1
Recommended resistor (E24)
150.0 Ω
Exact R
150.0 Ω
Voltage drop
3.00 V
Actual current / LED
20.00 mA
Min power rating
1/8 W
Formula
R = (Vsupply − V_led) / I = (5 − 2.0) / 0.0200 A = 150.00 Ω
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About this tool
- 1
Enter supply voltage
Input your power supply voltage (e.g., 5V for USB, 3.3V for microcontrollers, 12V for LED strips).
- 2
Enter LED specs
Input the LED forward voltage (Vf) and forward current (If). Common values: red ~2V/20mA, white ~3.2V/20mA.
- 3
Set LED count
Choose how many LEDs in series. The tool checks if your supply voltage is sufficient.
- 4
Get resistor value
View the calculated resistance, nearest standard resistor value, power dissipation, and a circuit diagram.
- Always check the LED datasheet for exact Vf and If ratings - typical values vary by color and type.
- Use a resistor rated for at least double the calculated power dissipation for reliability.
- If the nearest standard resistor is slightly higher, the LED will be slightly dimmer but safer.
- For multiple LEDs, series connection shares one resistor; parallel LEDs each need their own resistor.
- Calculates series resistor value with nearest E24 standard value suggestion
- Power dissipation calculation for proper resistor wattage selection
- Circuit diagram showing the resistor-LED connection
- Series and parallel LED configuration support
- Preset LED specs for common LED colors and types
- Adding indicator LEDs to an Arduino or Raspberry Pi project
- Designing LED circuits for hobby electronics or custom lighting
- Calculating resistors for automotive LED installations
- Teaching basic electronics - LED circuits are a classic first project