LED Resistor Calculator
Calculate the correct current-limiting resistor for your LED circuit
1LED Circuit Details
All LEDs share one resistor, same current flows through all
Check your LED datasheet (typically 1.8V-3.5V)
Standard LEDs: 20mA, High-power: 350mA+
All LEDs connected in a single chain
2Resistor Specifications
510Ω
Recommended Resistor
Calculated value: 500Ω
Min. Power Rating
500mW (1/2W)
Actual Current
19.6 mA
Power Dissipation
196.1 mW (0.196 W)
Circuit Diagram
Formula Reference
R = (Vs - Vf × n) / If
R = Resistance (Ohms)
Vs = Supply Voltage
Vf = LED Forward Voltage
n = Number of LEDs in series
If = LED Forward Current
Typical LED Forward Voltages
Why Do LEDs Need Current-Limiting Resistors?
LEDs are current-driven devices, not voltage-driven. Without a resistor to limit current, an LED will draw too much current from the power source, quickly overheating and burning out. The resistor ensures the LED receives the correct amount of current for safe, long-lasting operation.
How to Calculate LED Resistor Value
R = (Vs - Vf) / If
- • Vs = Your power supply voltage (e.g., 5V, 12V, 24V)
- • Vf = LED forward voltage from datasheet (varies by color)
- • If = Desired LED current (typically 20mA for standard LEDs)
The resistor drops the excess voltage that remains after the LED's forward voltage requirement is met. For multiple LEDs in series, multiply the forward voltage by the number of LEDs. Always choose a resistor with a power rating at least 2x the calculated dissipation.
Tips for LED Resistor Selection
- •Always use a resistor with higher power rating than calculated (2x recommended)
- •If exact resistor value isn't available, use the next higher standard value
- •For series LEDs, total forward voltage must be less than supply voltage
- •Consider using constant-current LED drivers for high-power applications