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LED Resistor Calculator

Calculate the perfect current-limiting resistor for your LED circuit. Enter your supply voltage, LED forward voltage, and desired current to get instant results with power dissipation warnings and standard resistor value suggestions.

Calculate Resistor Value

V
V

Typical: Red 2V, Green 2.2V, Blue/White 3.2V

mA

Typical: 10-20mA for standard LEDs

Calculated Resistance
150.00Ω
Nearest Standard Resistor (E24)
150.0Ω
Power Dissipation
60.00mW

Circuit Diagram

+
R
Resistor
LED
−
Formula
R = (Vs - Vf) / I
Vs = Supply Voltage
Vf = LED Forward Voltage
I = LED Current
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What is an LED Current-Limiting Resistor?

An LED current-limiting resistor is a resistor placed in series with an LED to control the amount of current flowing through it. LEDs are current-sensitive devices — too much current can damage or destroy them, while too little current results in dim or no light output.

Unlike incandescent bulbs, LEDs don't inherently limit their own current. When connected directly to a voltage source, they will draw excessive current and burn out almost instantly. A current-limiting resistor prevents this by dropping the excess voltage and restricting current flow to a safe level.

The Formula

R = (Vsupply - Vforward) / ILED
  • R = Required resistance (Ohms)
  • Vsupply = Supply voltage (Volts)
  • Vforward = LED forward voltage (Volts)
  • ILED = Desired LED current (Amps)

Why LED Resistors Matter

Prevents Burnout

Without a current-limiting resistor, LEDs will draw excessive current and burn out in seconds or even milliseconds.

Optimal Brightness

The right resistor ensures your LED operates at its rated current for maximum brightness and efficiency.

Extends Lifespan

Running LEDs at their proper current rating significantly extends their operational lifespan and reliability.

Common LED Forward Voltages

Different LED colors have different forward voltage drops. Use these typical values if you don't have your LED's datasheet.

LED ColorTypical Forward Voltage
Red
1.8 - 2.2V
Yellow
2.0 - 2.2V
Green
2.0 - 3.0V
Blue
3.0 - 3.5V
White
3.0 - 3.5V

Frequently Asked Questions

Common questions about this calculator and how to use it.

LEDs are current-sensitive devices that do not inherently limit their own current. Without a resistor, an LED connected directly to a voltage source will draw excessive current and burn out almost instantly. A current-limiting resistor drops the excess voltage and restricts current to a safe operating level.
Use the formula R = (Vsupply - Vforward) / ILED. Subtract the LED forward voltage from your supply voltage, then divide by your desired LED current in amps. For example, with a 5V supply, a red LED (2V forward voltage), and 20mA current: R = (5 - 2) / 0.02 = 150 ohms.
Red LEDs typically have a forward voltage between 1.8V and 2.2V. Yellow and orange LEDs are similar at 2.0-2.2V. Green LEDs range from 2.0-3.0V. Blue and white LEDs have higher forward voltages of 3.0-3.5V. Always check the LED datasheet for the exact value.
Using a resistor that is too small allows too much current to flow through the LED, which generates excess heat. This can cause the LED to burn out immediately or significantly reduce its lifespan. Always calculate the correct resistor value and check the power dissipation.
Power dissipation is the amount of heat generated by the resistor, calculated as P = I squared x R. Standard 1/4W (0.25W) resistors are the most common. If your calculated power dissipation exceeds 0.25W, you need a higher-wattage resistor (1/2W, 1W, or 2W) to prevent overheating.

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