FREE · CONSTRUCTION & TRADE CALCULATORS
LED Resistor Calculator.
Find the series resistor for one or several LEDs from the supply voltage, forward voltage and current, with its power rating.
Loading the calculator…
How to use LED Resistor Calculator
Enter the supply, pick an LED colour or type its forward voltage, set the current and how many LEDs are in series. The next standard resistor above the exact value is chosen.
How it works
R = (Vsupply − n × Vf) ÷ I, rounded up to the E12, E24 or E96 series; the rating is at least twice the dissipated power.
Example
A red LED (2 V, 20 mA) on 5 V needs 150 Ω, which dissipates 60 mW: a 1/8 W resistor is enough.
Questions about LED Resistor Calculator
Is LED Resistor Calculator free, and do I need an account?
Yes. This tool is free to use in your browser without an account. Processing takes place on your device.
What are the limits and what should I check?
For indicator LEDs. High-power LEDs need a constant-current driver. Everything is calculated in your browser; nothing you type is uploaded. Review the result before using it in your work.
Is my input sent to a server?
Your input is processed in your browser and is not uploaded by this tool. Files and pasted text are cleared when the page is refreshed. Normal website requests are still required to load the page and its libraries. Read the privacy explanation.