Meaning of numbers in col-md-4 , col-xs-1 , col-lg-2 in bootstrap
Here's an attempt at a simple explanation:
Ignoring the letters (xs, sm, md, lg) for now, I'll start with just the numbers…
- the numbers (1-12) represent a portion of the total width of any div
- all divs are divided into 12 columns
col-*-6spans 6 of 12 columns (half the width),
col-*-12spans 12 of 12 columns (the entire width), etc
So, if you want two equal columns to span a div, write
<div class="col-xs-6">Column 1</div> <div class="col-xs-6">Column 2</div>
Of if you want three unequal columns to span that same width, you could write:
<div class="col-xs-2">Column 1</div> <div class="col-xs-6">Column 2</div> <div class="col-xs-4">Column 3</div>
You'll notice the # of columns always add up to 12. It can be less than twelve, but beware if more than 12, as your offending divs will bump down to the next row (not
.row, which is another story altogether).
You can also nest columns within columns, (best with a
.row wrapper around them) such as:
<div class="col-xs-6"> <div class="row"> <div class="col-xs-4">Column 1-a</div> <div class="col-xs-8">Column 1-b</div> </div> </div> <div class="col-xs-6"> <div class="row"> <div class="col-xs-2">Column 2-a</div> <div class="col-xs-10">Column 2-b</div> </div> </div>
Each set of nested divs also span up to 12 columns of their parent div. NOTE: Since each
.colclass has 15px padding on either side, you should usually wrap nested columns in a
.row, which has -15px margins. This avoids duplicating the padding, and keeps the content lined up between nested and non-nested col classes.
— You didn't specifically ask about the
xs, sm, md, lg usage, but they go hand-in-hand so I can't help but touch on it…
In short, they are used to define at which screen size that class should apply:
- xs = extra small screens (mobile phones)
- sm = small screens (tablets)
- md = medium screens (some desktops)
- lg = large screens (remaining desktops)
You should usually classify a div using multiple column classes so it behaves differently depending on the screen size (this is the heart of what makes bootstrap responsive). eg: a div with classes
col-sm-4 will span half the screen on mobile phone (xs) and 1/3 of the screen on tablets(sm).
<div class="col-xs-6 col-sm-4">Column 1</div> <!-- 1/2 width on mobile, 1/3 screen on tablet) --> <div class="col-xs-6 col-sm-8">Column 2</div> <!-- 1/2 width on mobile, 2/3 width on tablet -->
NOTE: as per comment below, grid classes for a given screen size apply to that screen size and larger unless another declaration overrides it (i.e.
col-xs-6 col-md-4 spans 6 columns on
sm, and 4 columns on
lg, even though
lg were never explicitly declared)
NOTE: if you don't define
xs, it will default to
col-sm-6 is half the width on
lg screens, but full-width on
NOTE: it's actually totally fine if your
.row includes more than 12 cols, as long as you are aware of how they will react. –This is a contentious issue, and not everyone agrees.