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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 workbench
Circuit workbench

Keep RMS, peak and DC values distinct.

See the method

Enter circuit values

Runs on your device

Your 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.

Input reference and sample values

Use the units and choices shown for each field. Sample values are provided for practice, not as recommendations.

InputFormat and unitsSample
Supply voltageNumeric value. Unit: V. Must be greater than zero.5
LED forward voltageNumeric value. Unit: V. Zero or positive.2
Target currentNumeric value. Unit: mA. Must be greater than zero.20

Result for these sample inputs

150 Ω

Select Try the example in the form to load these values and calculate them again. This replaces the current form inputs. Compare the result with the method and worked explanation below.

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.

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