Find the Right Resistor for Any LED

A free browser-based LED resistor calculator that determines the correct current-limiting resistor for any LED circuit. Includes color presets with typical forward voltages, series and parallel array support, power dissipation warnings, and nearest E24 standard value matching.

How to Calculate an LED Resistor

Set supply voltage and LED specs

Enter the supply voltage (e.g. 5V, 12V) and select an LED color preset or enter custom Vf and If values.

Choose configuration

Select single LED, series (LEDs in a chain), or parallel (LEDs side by side). Set the number of LEDs.

Read the result

See the calculated resistance, nearest standard value, power dissipation, and any warnings about exceeding resistor ratings.

Calculate current-limiting resistors for single LEDs and arrays instantly

LED Color Presets

Supply Voltage (Vs)

LED Forward Voltage (Vf)

LED Forward Current (If) (mA)

Configuration

Result

Resistor Value

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Nearest E24

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Resistor Power

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Total Current

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Total Circuit Power

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Features

8 LED color presets (red, orange, yellow, green, blue, white, UV, IR) with typical Vf and If values Series and parallel array calculator — up to 20 LEDs with automatic resistor sizing Power dissipation warnings: ¼W, ½W, 1W thresholds with resistor rating recommendations Nearest E24 standard resistor value and interactive vector circuit diagram

FAQ

How is the LED resistor calculated?

R = (Vs - Vf) / If. For series LEDs: R = (Vs - n×Vf) / If. The supply voltage minus the total LED voltage drop, divided by the desired current.

What are typical LED forward voltages?

Red: 1.8-2.2V, Orange: 2.0-2.2V, Yellow: 2.0-2.4V, Green: 2.0-3.5V, Blue: 3.0-3.5V, White: 3.0-3.5V, UV: 3.3-3.8V, IR: 1.2-1.5V.

What is the difference between series and parallel?

Series: LEDs share the same current, voltages add up. You need Vs > sum of all Vf. Parallel: each LED has its own resistor (or shared with same Vf), current multiplies.

Why does the resistor get hot?

The resistor converts excess voltage to heat. P = (Vs-Vf)×If. If power exceeds the resistor rating (typically ¼W for small resistors), it can overheat and fail.

Can I run LEDs without a resistor?

Only if the supply voltage exactly matches the LED forward voltage. In practice, this is risky — even small voltage variations can destroy the LED. Always use a resistor.

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Who is this tool for?

🔌 Electronics Enthusiasts

Published 06 Apr 2026 Updated 21 May 2026