LED Resistor Calculator

Formula

(Vs−Vf)/I

Worked example

5V, 2V LED, 20mA — 150Ω

Quick answer

What does the LED Resistor Calculator do?

Calculate series resistor for an LED from supply voltage, forward voltage and desired current.

What is the LED Resistor Calculator?

Calculate series resistor for an LED from supply voltage, forward voltage and desired current. Use it when you have the required inputs and want a deterministic, repeatable result with the calculation method visible.

How to use this calculator

Enter the values requested by the tool, keep units and time periods consistent, resolve any validation message, calculate, then review the primary answer together with the displayed formula and supporting values.

Formula and method

This calculator uses the deterministic formula (Vs−Vf)/I. Enter the required values, then review the displayed substitution and result breakdown to verify the calculation.

Worked example

5V, 2V LED, 20mA 150Ω

Common mistakes to avoid

Check units, decimal points, percentages, signs, date/time order, selector choices, and rounding. For important decisions, verify the result against an independent source or qualified professional when appropriate.