LED Resistor Calculator

Calculate the correct series resistor value for an LED circuit.

Supply Voltage Vcc (V)

LED Forward Voltage Vf (V)

Forward Current If (mA)

Common LED presets:

Exact Value

150.0 Ω

Nearest E12

150.0 Ω

Nearest E24

150.0 Ω

Circuit Details

Voltage across R

3.00 V

Voltage across LED

2.00 V

Power in resistor

60.00 mW

Wattage rating

1/8 W min.

ASCII Circuit

  Vcc (5V)
    │
   [R] 150.0 Ω (E24)
    │
   [▶] LED Vf=2.0V
    │
   GND

About LED Resistor Calculator

Every LED needs a current-limiting resistor in series to prevent it from burning out. The formula is simple: R = (Vcc − Vf) / If, where Vcc is the supply voltage, Vf is the LED forward voltage, and If is the desired forward current in amps. Typical LEDs run at 20 mA (0.020 A). The E12 and E24 series are standard resistor values available from manufacturers — always use the nearest higher standard value to keep current within the LED's rated limit. Check the power rating: a 1/4 W resistor handles up to 250 mW.

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