LED Resistor Calculator
Calculate the correct resistor value for your LED circuit to ensure safe operation and optimal brightness.
Calculated Result
Interactive Circuit
Understanding LED Resistor Calculation
To protect an LED from excessive current, we need to calculate the correct resistor value using Ohm's Law:
R = (Vs - Vf) / If
Where:
- R = Required resistor value (Ω)
- Vs = Source voltage (V)
- Vf = LED forward voltage (V)
- If = Forward current (A)
P = (Vs - Vf) × If
Where:
- P = Power dissipated by resistor (W)
- Vs = Source voltage (V)
- Vf = LED forward voltage (V)
- If = Forward current (A)
Source Voltage
Power supply voltage (e.g., 5V, 3.3V)
Forward Voltage
LED voltage drop (varies by color)
Forward Current
LED current rating (typically in mA)
LED Circuit Design Guide
LED Forward Voltage by Color
Common Colors
- Red: 1.8V - 2.2V
- Green: 2.0V - 2.4V
- Blue: 2.8V - 3.3V
- Yellow: 1.9V - 2.3V
- White: 2.8V - 3.3V
Typical Current Ratings
- Standard LED: 20mA
- Low-power LED: 2mA - 5mA
- High-brightness LED: 30mA - 70mA
- Super-bright LED: 70mA - 150mA
- Power LED: 350mA - 1000mA
Common Mistakes to Avoid
No Current-Limiting Resistor
Never connect an LED directly to a voltage source without a resistor - it will likely be destroyed instantly.
Wrong Voltage Values
Using incorrect forward voltage for LED color or wrong power supply voltage will lead to improper brightness or damage.
Tips for Success
Check Polarity
LEDs only work in one direction. The longer lead is usually positive (anode).
Power Rating
Choose a resistor with at least twice the calculated power rating for safety.
Testing
Start with a higher resistance and adjust down if needed for desired brightness.
Multiple LED Configurations
Series Connection
- • Add forward voltages together
- • Same current through all LEDs
- • Higher supply voltage needed
- • One resistor for the chain
Parallel Connection
- • Same voltage across all LEDs
- • Each LED needs its own resistor
- • Total current is sum of all LEDs
- • More consistent brightness