Embed the LED Resistor Calculator
The series resistor an LED needs, from supply voltage, forward voltage and current — with the power it must dissipate and which standard value to pick. Set the values it should open on, then copy the iframe. Your visitors can change them; the widget recomputes against Rule Calculator and never touches your page.
Opening values
Set what the widget shows before anyone touches it. Leave a field as it is and it stays out of the URL.
Preview
Paste this
<iframe src="https://rulecalculators.com/embed/led-resistor" width="100%" height="840" style="border:1px solid #e5e5e5;border-radius:12px" loading="lazy" title="LED Resistor Calculator"></iframe>
<p style="font:13px/1.5 system-ui,sans-serif;color:#666;margin:6px 0 0"><a href="https://rulecalculators.com/calc/led-resistor" style="color:#666">LED Resistor Calculator</a> by <a href="https://rulecalculators.com" style="color:#666">Rule Calculator</a></p>Free for commercial use. The one condition is the credit link inside the widget, which is how the calculator stays free. Want the numbers in your own markup instead? The same calculator is a JSON endpoint, or see the full LED Resistor Calculator page with its sources and working.