css - What are the difference between col-lg and col-md in bootstrap3

Question

What are the difference between col-lg, col-md ,col-xs and col-sm grid system in in bootstrap 3.

In a bootstrap template they used <div class="col-lg-6 col-md-6 col-xs-12 col-sm-6"></div> only for one column grid. I am a beginner in Bootstrap.

Answer 1

When using Bootstrap those are the classes which are added for one column grid and correspond to extra small, small, medium and large devices.

.col-xs = *Extra small devices (ie Phones) (<768px)

.col-sm = Small devices (ie Tablets) (≥768px)

.col-md = Medium devices (ie laptops, or small desktops) (≥992px)

.col-lg = Large devices (ie Desktops) (≥1200px)*

This way through media queries you can allow to have only the right classes interpreted by the browser. If you surf that website from a tablet for example, you will see that the css properties which are actually applied in the browser are only the ones for the .col-sm class.

UPDATE

Also it's important to mention that those classes are used on a grid of 12 columns in total which is the grid system setup used by Bootstrap.

Therefore when you are using .col-sm-4 on an element it means that the element will take 4 columns out of 12 of the total width. Which logically means that if .col-sm-4 is used then only 3 elements per row can fit into the page on tablet.

For example, let's say we want to show some project cards for a portfolio:

<div class="col-xs-12 col-sm-6 col-md-4 col-lg-3 card">
    <div class="card-wrapper">  
        <img src="img.jpg">
        <div class="overlay-text">
            <h5>Project 1</h5>
            <div class="labels">
                <label>Tech Stack</label>
                <h6>HTML5, CSS, JS</h6>
            </div>       
        </div>          
    </div> 
</div> 

Using class="col-xs-12 col-sm-6 col-md-4 col-lg-3" all at the same time is used to activate different CSS properties on an element when viewing the page on a particular device.

In other terms, if the user opens the site on a desktop, col-lg-3 means that a total of 4 cards will be displayed, when col-md-4 means a total of 3 cards, col-sm-6 a total of 2 cards and then col-xs-12 means on mobile only 1 card will with 100% width of the page.