CSS Absolute and Relative Units

CSS Web Development Front End Technology

Both CSS Absolute Units and Relative Units fall under the category Distance units.

CSS Relative Units define a length of an element in reference to another element.

For example, vh relative unit is relative to viewport height.

Following are the CSS relative units −

Sr.No	Unit & Relative to
1	% Parent element dimensions
2	em Font size of the element
3	ex x-height of the element's font
4	lh Line height of the element
5	rem Font size of the root element
6	rlh Line height of the root element
7	vb 1% of viewport's size in the root element's block axis
8	vh 1% of viewport's height
9	vmax 1% of viewport's larger dimension
10	vmin 1% of viewport's smaller dimension
11	vw 1% of viewport's width

Example

Let us see an example for CSS relative units −

Live Demo

<!DOCTYPE html>
<html>
<head>
<title>CSS Relative Units</title>
<style>
html{
   font-size: 14px;
   line-height: normal;
}
form {
   width:70%;
   margin: 0 auto;
   text-align: center;
}
* {
   padding: 2px;
   margin:5px;
}
input[type="button"] {
   border-radius: 10px;
}
#textContain {
   font-size: 20px;
   line-height: 2;
}
</style>
</head>
<body>
<form>
<fieldset>
<legend>CSS-Relative-Units</legend>
<input type="text" id="textSelect" placeholder="Type Text Here...">
<input type="number" id="numSelect" value="1" min="1">
<div id="radioBut">
<input class="radio" type="radio" name="heading" value="em" checked><label>em</label>
<input class="radio" type="radio" name="heading" value="rem"><label>rem</label>
<input class="radio" type="radio" name="heading" value="vw"><label>vw</label>
<input class="radio" type="radio" name="heading" value="vh"><label>lh</label>
<input class="radio" type="radio" name="heading" value="ex"><label>ex</label>
</div>
<div id="textContain">Text Preview: <span id="textPreview">Output will show up here</span></div>
<input type="button" onclick="changeText()" value="Preview">
</fieldset>
</form>
<script>
var textSelect = document.getElementById("textSelect");
var numSelect = document.getElementById("numSelect");
var textPreview = document.getElementById("textPreview");
function changeText() {
   if(textSelect.value === '')
      textPreview.textContent = 'Type some text first';
   else{
      for(var i=0; i<5; i++){
         var radInp = document.getElementsByClassName('radio')[i];
         if(radInp.checked === true){
            textPreview.textContent = textSelect.value;
            textPreview.style.fontSize = numSelect.value+radInp.value
         }
      }
   }
}
</script>
</body>
</html>

Output

Following is the output for above code −

Before clicking any button −

After clicking ‘Preview’ button with ‘em’ option selected and empty text field −

After clicking ‘Preview’ button with ‘rem’ option selected and non-empty text field −

After clicking ‘Preview’ button with ‘em’ option selected and non-empty text field −

Following are the CSS absolute units −

Sr.No	Unit & Name
1	cm Centimeters (1 cm = 100 mm)
2	in Inches (1 in = 2.54 cm)
3	mm Millimeters
4	pc Picas (1 pc = 12 pt)
5	pt Points (1 pt = 1/72 in)
6	px Pixels (1 px = 0.75 pt)

Example

Let us see an example for CSS absolute units −

Live Demo

<!DOCTYPE html>
<html>
<head>
<title>CSS Absolute Units</title>
<style>
form {
   width:70%;
   margin: 0 auto;
   text-align: center;
}
* {
   padding: 2px;
   margin:5px;
}
input[type="button"] {
   border-radius: 10px;
}
</style>
</head>
<body>
<form>
<fieldset>
<legend>CSS-Absolute-Units</legend>
<input type="text" id="textSelect" placeholder="Type Text Here...">
<input type="number" id="numSelect" value="10" min="1">
<div id="radioBut">
<input class="radio" type="radio" name="heading" value="pc"><label>pc</label>
<input class="radio" type="radio" name="heading" value="pt"><label>pt</label>
<input class="radio" type="radio" name="heading" value="px" checked><label>px</label>
<input class="radio" type="radio" name="heading" value="in"><label>in</label>
<input class="radio" type="radio" name="heading" value="cm"><label>cm</label>
</div>
<div id="textContain">Text Preview: <span id="textPreview">Output will show up here</span></div>
<input type="button" onclick="changeText()" value="Preview">
</fieldset>
</form>
<script>
var textSelect = document.getElementById("textSelect");
var numSelect = document.getElementById("numSelect");
var textPreview = document.getElementById("textPreview");
function changeText() {
   if(textSelect.value === '')
      textPreview.textContent = 'Type some text first';
   else{
      for(var i=0; i<5; i++){
         var radInp = document.getElementsByClassName('radio')[i];
         if(radInp.checked === true){
            textPreview.textContent = textSelect.value;
            textPreview.style.fontSize = numSelect.value+radInp.value
         }
      }
   }
}
</script>
</body>
</html>