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Electrical

LED Series Resistor Calculator

Estimate a resistor for an ideal LED voltage-drop model.

Ideal component relationshipsUnits and assumptions explained below

Circuit parameters

Runs on your device

CIRCUIT RESULT

Your result

Let’s calculate.

Use the Calculate button to see your result.

Review the method below for assumptions and conventions.

How to use this tool

  1. Enter supply voltage, led forward voltage, target current.
  2. Select Calculate to view the result.
  3. Check the method and assumptions below before using the result.

The method, explained

Resistance = (supply − forward voltage)/(target mA/1000).

A WORKED EXAMPLE

Using supply voltage = 5 V, led forward voltage = 2 V, target current = 20 mA, the result is 150 Ω. Change these example inputs to match your task; use the method above to check each step.

What to keep in mind

Confirm LED current limits and resistor power rating from component datasheets. Ideal-component calculation for study and estimation. It does not select safe wiring, protective devices or component ratings for an installation.

Common questions

Which inputs does this calculation need?

Estimate a resistor for an ideal LED voltage-drop model. Enter supply voltage in V, led forward voltage in V, target current in mA. The filled example is editable and is not a saved personal record.

How should I interpret the result?

Confirm LED current limits and resistor power rating from component datasheets. Ideal-component calculation for study and estimation. It does not select safe wiring, protective devices or component ratings for an installation.

Methodology maintained by ClarityKit. How these tools are built and checked.