Is embedding the LED resistor calculator free?

Yes. It is free to embed on any site, with no account, no API key and no usage limits. The whole calculation runs in your visitor’s own browser, so there is no server cost — we only ask that you keep the small "LED Resistor Calculator by LK Forge" credit line that comes with the embed code.

What can visitors do with the embedded calculator?

They set the supply voltage, the LED’s forward voltage and forward current, and how many LEDs in series or parallel. The tool returns the current-limiting resistor, the nearest standard value, the power it dissipates and a safe wattage rating, and the total current — with a schematic whose LEDs glow when the supply is enough.

What formula does it use?

R = (Vsupply − Vf) / If, extended to R = (Vsupply − n·Vf) / If for n LEDs in series. It is Ohm’s law applied to the voltage the resistor must drop, and it warns when the supply is below the LED forward voltage so the LEDs cannot light.

What iframe height should I use, especially on mobile?

The snippet ships with height="760", which fits the schematic, the sliders and the readouts without clipping even on a narrow phone where they stack into one column. On a wider page the widget centres within its max-width of 560px. That single height works across screen sizes.

Where can I embed it — WordPress, Wix, Squarespace, Notion?

Anywhere you can add HTML, because it is a standard iframe. In WordPress use a Custom HTML block; in Squarespace a Code/Embed block; in Wix an Embed HTML element; in Ghost an HTML card; in Notion paste the /embed/led-resistor/ URL. On a plain HTML page, paste the snippet straight into the markup.

Does the embedded calculator track visitors or set cookies?

No. Everything runs locally in the visitor’s browser — nothing is uploaded. The embed sets no tracking cookies and sends no analytics, so it is safe on a privacy-sensitive site, an intranet, or a page for students.

Widgets

How to Add an LED Resistor Calculator to Your Website

LK Forge · 4 min read · Updated September 2026

You can add a full LED current-limiting resistor calculator to any website, blog, or classroom page with a single line of code — free, with no sign-up, no plugin, and no script to install. Visitors size the resistor their LED needs. This guide covers the fastest way to embed the LED Resistor Calculator, what it teaches, and where it works.

The quickest way: paste one embed snippet

An embed is just an <iframe> that loads the calculator from lkforge.com, plus a small credit line. Copy this into your page’s HTML where you want the widget to appear:

<iframe src="https://lkforge.com/embed/led-resistor/"
        width="100%" height="760" loading="lazy"
        style="border:0;max-width:560px"
        title="LED Resistor Calculator by LK Forge"></iframe>
<p><a href="https://lkforge.com/tools/physics/led-resistor/">LED Resistor Calculator</a>
   by <a href="https://lkforge.com/">LK Forge</a></p>

The <iframe> is the live calculator; the <p> underneath is a plain credit link. Keep that line — the visible link is what keeps the widget free to embed. You can also copy this exact code from the LK Forge widget gallery.

What the widget shows

The calculator opens on a common case so a visitor sees a resistor value at once and can then change it:

Supply, Vf and If: set the supply voltage, the LED forward voltage and target current.
Series or parallel: choose the arrangement and the number of LEDs.
Live schematic: the LEDs glow when the supply is enough, and grey out with a warning when it isn’t.
Readouts: exact resistor value, nearest standard value, power and a safe rating, and total current.

Where it works

Because it is a standard iframe, the embed works anywhere you can add HTML — WordPress (Custom HTML block), Squarespace (Code block), Wix (Embed HTML), Ghost (HTML card), Notion (paste the /embed/led-resistor/ URL), or a plain HTML page. Copy the embed code from the widget gallery and paste it wherever a lesson or a maker post needs LED resistors students can size themselves.

Grab the embed code from the LK Forge widget gallery — free, no sign-up.

Open the LED Resistor Calculator

Frequently asked questions

Is embedding the LED resistor calculator free?: Yes. It is free to embed on any site, with no account, no API key and no usage limits. The whole calculation runs in your visitor’s own browser, so there is no server cost — we only ask that you keep the small "LED Resistor Calculator by LK Forge" credit line that comes with the embed code.
What can visitors do with the embedded calculator?: They set the supply voltage, the LED’s forward voltage and forward current, and how many LEDs in series or parallel. The tool returns the current-limiting resistor, the nearest standard value, the power it dissipates and a safe wattage rating, and the total current — with a schematic whose LEDs glow when the supply is enough.
What formula does it use?: R = (Vsupply − Vf) / If, extended to R = (Vsupply − n·Vf) / If for n LEDs in series. It is Ohm’s law applied to the voltage the resistor must drop, and it warns when the supply is below the LED forward voltage so the LEDs cannot light.
What iframe height should I use, especially on mobile?: The snippet ships with height="760", which fits the schematic, the sliders and the readouts without clipping even on a narrow phone where they stack into one column. On a wider page the widget centres within its max-width of 560px. That single height works across screen sizes.
Where can I embed it — WordPress, Wix, Squarespace, Notion?: Anywhere you can add HTML, because it is a standard iframe. In WordPress use a Custom HTML block; in Squarespace a Code/Embed block; in Wix an Embed HTML element; in Ghost an HTML card; in Notion paste the /embed/led-resistor/ URL. On a plain HTML page, paste the snippet straight into the markup.
Does the embedded calculator track visitors or set cookies?: No. Everything runs locally in the visitor’s browser — nothing is uploaded. The embed sets no tracking cookies and sends no analytics, so it is safe on a privacy-sensitive site, an intranet, or a page for students.