LED Resistor Calculator for Single LEDs and Arrays

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

1
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.

2
Choose configuration

Select single LED, series (LEDs in a chain), parallel (LEDs side by side), or the series-parallel matrix — several series strings in parallel, one resistor per string. Set the number of LEDs.

3
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
Vs R = ? LED I = ?
Result
Resistor Value
—
Nearest E24
—
Resistor Power
—
Total Current
—
Total Circuit Power
—
Resistors needed
—
⚠️

Features

8 LED color presets (red, orange, yellow, green, blue, white, UV, IR) with typical Vf and If values
Each preset loads a realistic forward voltage — about 1.8–2.2V for red, 3.0–3.5V for blue and white — so you skip looking up the datasheet.
Series and parallel array calculator — up to 20 LEDs with automatic resistor sizing
Applies R = (Vs − n×Vf) / If for series chains and sizes the limiting resistor for the whole array automatically.
Power dissipation warnings: ¼W, ½W, 1W thresholds with resistor rating recommendations
Computes P = (Vs − Vf) × If and flags when to step up from a ¼W to a ½W, 1W or heatsinked 2W resistor.
Nearest E24 standard resistor value and interactive vector circuit diagram
Rounds the exact ohms to the closest purchasable E24 value and draws the circuit as a scalable SVG schematic.

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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🔌 Electronics Enthusiasts
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