JSFiddle - React, Tailwind, and code Playground

by Yaroslav Samardak

HTML

<div id='cm1'></div>
<div id='cm3'></div>
<div id='cm5'></div>
<div id='cm10'></div>

CSS

body {
  padding: 0;
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";
}

div {
  display: block;
  height: 1px;
  background-color: #F00;
  position: relative;
  margin: 16px 8px;
}

div:after {
  content: attr(data-value);
  position: absolute;
  width: 10rem;
  height: 1rem;
  line-height: 1rem;
  left: 100%;
  margin-left: 8px;
  top: -0.5rem;
}

#cm1 {
  width: 1cm;
}
#cm3 {
  width: 3cm;
}
#cm5 {
  width: 5cm;
}
#cm10 {
  width: 10cm;
}

JavaScript

[1, 3, 5, 10].forEach((s) => {
	const el = document.getElementById(`cm${s}`)
  const px = window.devicePixelRatio * el.offsetWidth
  el.setAttribute('data-value', `In ${s}cm — ${px}px`)
})


const dpi = (function () {
    for (var i = 56; i < 2000; i++) {
        if (
        	matchMedia("(max-resolution: " + i + "dpi)").matches === true ||
          matchMedia("(-webkit-max-device-pixel-ratio: " + i + "dpi)").matches === true
        ) {
            return i;
        }
    }
    return i;
})();

const px = dpi / 2.54
alert(`${px}px, ${dpi}dpi, ${window.devicePixelRatio}dpr`)