CSS - Width property (of a box)


The width property specifies the width of boxes and it's calculation is defined by the box sizing property.

Width HTML vs CSS attribute

Don't be confuse ! This is not the same attribute than the HTML width attribute that is only limited to an handful of HTML element such as img, iframe, …

If you want to set a width on a p element for instance,

  • you need to use the css width attribute
<p style="width:80px;border:1px solid aqua;">
This paragraph will be constraint by the CSS width.
<p width="80px" style="border:1px solid aqua;">
This paragraph will not follow the width HTML attribute


The following property have an effect on the width calculation:

  • The box sizing property defines the calculation.
  • The min-width and max-width properties override width.
  • The white space property may prevents a line box to (wrap|break)
  • The type of block: An inline block will not take the width into account.

Formula taking into account only the box sizing property:

<MATH> \text{Width Size} = \text{Content Size} </MATH>

<MATH> \text{Width Size} = \text{Content Size} + \text{Padding Size} + \text{Border Size} </MATH>


Values 	<length> | <percentage> | auto | inherit
Initial value 	auto
Applies to 	All elements but non-replaced inline elements, table rows, and row groups
Inherited 	No 



Box Sizing

Inline vs Block Box

.coloredBox {
	width: 20px; 
	height: 20px; 
	border-left: 4px solid aqua;
	border-right: 4px solid red;
	border-bottom: 4px solid black;
	border-top: 4px solid blue;
  • The type of block is important. It must be block box
<p>A block box</p>
<span class="coloredBox"></span>

<p>A inline box will not respond to the width</p>
<span class="coloredBox" style="display:inline"></span>

The p element renders by default as a block box whereas the span element renders default as a inline box

Documentation / Reference

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