LED Resistor Calculator
Design LED circuits with the correct resistor values. Get instant calculations and visualize your circuit in real-time.
Choose Circuit Type
Select the circuit configuration for your LED project.
Single current path with one resistor for all LEDs.
Multiple current paths, each LED has its own resistor.
Multiple series strings connected in parallel.
Power Supply & LED Details
Set your power supply voltage and LED specifications.
Power Supply
LED Selection
LED Configuration
Specify how many LEDs you want in your circuit.
LED Arrangement
Circuit Preview
Resistor Values
Power & Voltage
LED Circuit Reference
Series Connection
- Benefits: Same current through all LEDs, uses only one resistor
- Limitations: Requires higher supply voltage, if one LED fails, all LEDs go out
- Formula: R = (Vsupply - (n × Vled)) / Iled
- Best for: Simple circuits with few LEDs, consistent brightness
Parallel Connection
- Benefits: Works with lower supply voltage, if one LED fails others stay lit
- Limitations: Requires individual resistors for each LED, higher current draw
- Formula: R = (Vsupply - Vled) / Iled (for each LED)
- Best for: Reliability, where some LEDs can be allowed to fail
Series-Parallel Connection
- Benefits: Balance of advantages from both series and parallel
- Limitations: More complex design
- Formula: R = (Vsupply - (n × Vled)) / Iled (for each string)
- Best for: Large LED arrays, efficient power usage
| LED Color | Forward Voltage (Vf) | Typical Current | Wavelength |
|---|---|---|---|
| Red | 1.8-2.2V | 20mA | 620-660nm |
| Green | 2.0-2.2V | 20mA | 520-550nm |
| Blue | 2.9-3.4V | 20mA | 460-490nm |
| White | 2.9-3.4V | 20mA | Full spectrum |
| Yellow | 2.0-2.2V | 20mA | 585-595nm |
E12 Series (±10% tolerance)
Values are multiplied by powers of 10: Ω, 10Ω, 100Ω, 1kΩ, etc.
Wattage Selection
- Common Ratings: 1/8W, 1/4W, 1/2W, 1W, 2W
- Choose a wattage rating at least twice the calculated power
- The calculator will recommend the appropriate wattage
Why do LEDs need resistors?
LEDs need resistors to limit current flow. Without a resistor, the LED would draw excessive current and burn out quickly. The resistor maintains the appropriate current level for safe and efficient operation.
What happens if I use the wrong resistor value?
Too low: The LED will be brighter but may overheat and fail prematurely.
Too high: The LED will be dimmer than expected but will still function safely.
Can I use one resistor for multiple LEDs in parallel?
It's not recommended. Each parallel LED should have its own current-limiting resistor to ensure even current distribution and prevent cascading failures.