💡 LED Resistor Calculator

Calculate the correct resistor value for your LED circuit

📏 Input Parameters

Source Voltage (V)

LED Forward Voltage (V)

LED Current (mA)

📊 Results

Required Resistor Value

500 Ω

Power Rating (Minimum)

0.20 W

📚 Understanding LED Resistors

Why Do LEDs Need Resistors?

LEDs require a current-limiting resistor to prevent excessive current flow that could damage the LED. The resistor drops the excess voltage and limits current to a safe level.

Formula

R = (Vs - Vf) / I

R: Resistor value in ohms (Ω)
Vs: Source voltage
Vf: LED forward voltage
I: LED current in amperes

Power Rating

P = (Vs - Vf) × I

Always use a resistor with a power rating at least 2x the calculated value for safety.

Typical LED Forward Voltages

Red: 1.8-2.2V
Green: 2.0-2.2V
Blue: 3.0-3.4V
White: 3.0-3.4V
Yellow: 2.0-2.2V

Frequently Asked Questions

What happens if I don't use a resistor with an LED?

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Without a current-limiting resistor, excessive current will flow through the LED, causing it to overheat and fail almost immediately. Always use an appropriate resistor.

Can I use a higher resistance value?

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Yes, using a higher resistance value is safe but will result in dimmer LED brightness. Using a lower value may damage the LED.

What power rating should I use for the resistor?

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Use a resistor with at least 2x the calculated power rating. For most LED circuits, a 1/4W (0.25W) resistor is sufficient.