LED Resistor Calculator
Calculate the ideal resistor value and power rating to protect LEDs in series and parallel circuits
Calculate LED Resistor Value
Total number of LEDs in the circuit
DC voltage of your power source
Common LED forward voltages
Voltage drop across one LED
Current through each LED (typically 20mA for standard LEDs)
Resistor Calculation Results
Circuit Details
Circuit Type
Series
Total Voltage Drop
2.0V
Total Current
20mA
Resistor Voltage
3.0V
Power Analysis
Power per LED
0.040W
Total LED Power
0.040W
Resistor Power
0.060W
Circuit Diagrams
Series Connection
Same current through all LEDs
Parallel Connection
|——LED——|
+——LED——+—— V-
Same voltage across all LEDs
Example Calculation
Red LED Example
Supply voltage: 12V
LED voltage: 2.0V (Red)
LED current: 20mA
Number of LEDs: 3 (Series)
Calculation
R = (V - n × Vₒ) / Iₒ
R = (12V - 3 × 2.0V) / 0.02A
R = (12V - 6V) / 0.02A
R = 300Ω
Power = I² × R = 0.02² × 300 = 0.12W
Use 0.25W resistor
LED Color Voltages
LED Tips
Always use a resistor to limit current
Use at least 2× power rating for safety
Check LED polarity (long leg = positive)
Standard LEDs typically use 20mA
For high-power LEDs, use constant current drivers
Understanding LED Resistor Calculations
Why Do LEDs Need Resistors?
LEDs are current-sensitive devices. Without current limiting, they can draw excessive current and burn out instantly. A resistor in series limits the current to safe levels, ensuring the LED operates within its specifications.
How It Works
- •The resistor drops excess voltage
- •Limits current to LED's safe operating range
- •Prevents thermal damage and extends LED life
- •Maintains consistent brightness
Series vs Parallel
Series Connection
R = (V - n × Vₒ) / Iₒ
- • Same current through all LEDs
- • Voltages add up
- • One resistor for all LEDs
- • If one fails, all go out
Parallel Connection
R = (V - Vₒ) / (n × Iₒ)
- • Same voltage across all LEDs
- • Currents add up
- • One resistor (not recommended for multiple LEDs)
- • Better to use individual resistors
⚠️ Important Notes
- • Never connect LEDs directly to power
- • Always check LED polarity
- • Use proper wattage resistors
- • For parallel LEDs, use individual resistors
✓ Best Practices
- • Use 100% power derating (2× wattage)
- • Start with manufacturer specifications
- • Test with lower currents first
- • Use constant current drivers for high-power LEDs
📋 Standard Values
- • Standard LED current: 20mA
- • High-brightness LEDs: 350mA+
- • Common supply voltages: 5V, 12V, 24V
- • Standard resistor wattages: 0.25W, 0.5W, 1W