What is the difference among col-lg-*, col-md-* and col-sm-* in Bootstrap?

Solution 1:

Updated 2020...

Bootstrap 5

In Bootstrap 5 (alpha) there is a new -xxl- size:

col-* - 0 (xs)
col-sm-* - 576px
col-md-* - 768px
col-lg-* - 992px
col-xl-* - 1200px
col-xxl-* - 1400px

Bootstrap 5 Grid Demo

Bootstrap 4

In Bootstrap 4 there is a new -xl- size, see this demo. Also the -xs- infix has been removed, so smallest columns are simply col-1, col-2.. col-12, etc..

col-* - 0 (xs)
col-sm-* - 576px
col-md-* - 768px
col-lg-* - 992px
col-xl-* - 1200px

Bootstrap 4 Grid Demo

Additionally, Bootstrap 4 includes new auto-layout columns. These also have responsive breakpoints (col, col-sm, col-md, etc..), but don't have defined % widths. Therefore, the auto-layout columns fill equal width across the row.

Bootstrap 3

The Bootstrap 3 grid comes in 4 tiers (or "breakpoints")...

• Extra small (for smartphones .col-xs-*)
• Small (for tablets .col-sm-*)
• Medium (for laptops .col-md-*)
• Large (for laptops/desktops .col-lg-*).

These grid sizes enable you to control grid behavior on different widths. The different tiers are controlled by CSS media queries.

So in Bootstrap's 12-column grid...

col-sm-3 is 3 of 12 columns wide (25%) on a typical small device width (> 768 pixels)

col-md-3 is 3 of 12 columns wide (25%) on a typical medium device width (> 992 pixels)

The smaller tier (xs, sm or md) also defines the size for larger screen widths. So, for the same size column on all tiers, just set the width for the smallest viewport...

<div class="col-lg-3 col-md-3 col-sm-3">..</div> is the same as,

<div class="col-sm-3">..</div>

Larger tiers are implied. Because col-sm-3 means 3 units on sm-and-up, unless specifically overridden by a larger tier that uses a different size.

xs(default) > overridden by sm > overridden by md > overridden by lg

Combine the classes to use change column widths on different grid sizes. This creates a responsive layout.

<div class="col-md-3 col-sm-6">..</div>

The sm, md and lg grids will all "stack" vertically on screens/viewports less than 768 pixels. This is where the xs grid fits in. Columns that use the col-xs-* classes will not stack vertically, and continue to scale down on the smallest screens.

Resize your browser using this demo and you'll see the grid scaling effects.

This article explains more about how the Bootstrap grid

Solution 2:

The bootstrap docs do explain it, but it still took me a while to get it. It makes more sense when I explain it to myself in one of two ways:

If you think of the columns starting out horizontally, then you can choose when you want them to stack.

For example, if you start with columns: A B C

You decide when should they stack to be like this:

A

B

C

If you choose col-lg, then the columns will stack when the width is < 1200px.

If you choose col-md, then the columns will stack when the width is < 992px.

If you choose col-sm, then the columns will stack when the width is < 768px.

If you choose col-xs, then the columns will never stack.

On the other hand, if you think of the columns starting out stacked, then you can choose at what point they become horizontal:

If you choose col-sm, then the columns will become horizontal when the width is >= 768px.

If you choose col-md, then the columns will become horizontal when the width is >= 992px.

If you choose col-lg, then the columns will become horizontal when the width is >= 1200px.

Solution 3:

From Twitter Bootstrap documentation:

• small grid (≥ 768px) = .col-sm-*,
• medium grid (≥ 992px) = .col-md-*,
• large grid (≥ 1200px) = .col-lg-*.