LED Resistor Calculator

Calculate the current limiting resistor for LED circuits.

Common LED Types (click to select)

LED Connection

Supply Voltage

LED Forward Voltage (Vf)

LED Current (If)

Typical: 10-20mA for standard, 350mA+ for high power

Number of LEDs

Circuit Diagram

Recommended Resistor

Actual Current

20.0 mA

Power Dissipation

60 mW

Resistor Rating

0.125W min

Voltage Headroom

3.0V

Formula

R = (V_supply - V_LED) / I_LED

For series LEDs: V_LED = V_f × number of LEDs

Why LEDs Need Resistors

LEDs are current-driven devices. Without a current limiting resistor, they will draw excessive current and burn out almost instantly. The resistor drops the excess voltage and limits current to a safe level.

Key Parameters

Forward Voltage (Vf): Voltage drop across LED when lit
Forward Current (If): Operating current (typically 10-20mA)
Max Current: Don't exceed or LED will fail
Power Rating: Resistor must handle the heat

Series vs Parallel

Series: Same current through all LEDs, higher voltage needed
Parallel: Lower voltage, but unequal current distribution
Best Practice: Series with individual resistors per LED string

Typical LED Forward Voltages

LED Color	Forward Voltage	Typical Current	Notes
Infrared	1.2-1.6V	20-100mA	Not visible
Red	1.8-2.1V	10-20mA	Most efficient
Orange	2.0-2.2V	10-20mA	-
Yellow	2.0-2.2V	10-20mA	-
Green	2.0-3.0V	10-20mA	Wide range
Blue	3.0-3.5V	10-20mA	Higher Vf
White	3.0-3.5V	10-20mA	Blue + phosphor
UV	3.0-4.0V	20mA	Eye hazard

Related Tools

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Resistor Color Code

Power Dissipation