Bootstrap 4 Grid Extra Small
Extra Small Grid Example
| Extra small | Small | Medium | Large | Extra Large | |
|---|---|---|---|---|---|
| Class prefix | .col- | 
    .col-sm- | 
    .col-md- | 
    .col-lg- | 
    .col-xl- | 
  
| Screen width | <576px | >=576px | >=768px | >=992px | >=1200px | 
Assume we have a simple layout with two columns. We want the columns to split 25%/75% for ALL devices.
We will add the following classes to our two columns:
<div class="col-3">....</div>
<div class="col-9">....</div>
The following example will result in a 25%/75% split on all devices (extra small, small, medium, large and xlarge).
Example
 <div class="container-fluid">
  <div class="row">
      <div class="col-3 bg-success">
      <p>Lorem ipsum...</p>
    </div>
      <div class="col-9 bg-warning">
      <p>Sed ut perspiciatis...</p>
    </div>
  </div>
 </div>
Try it Yourself »Note: Make sure that the sum adds up to 12 or fewer (it is not required that you use all 12 available columns):
For a 33.3%/66.6% split, you would use .col-4 and .col-8 (and for a 50%/50% split, you would use .col-6 and .col-6):
Example
  <!-- 33.3%/66.6% split -->
<div class="container-fluid">
  <div class="row">
      <div class="col-4 bg-success">
      <p>Lorem ipsum...</p>
    </div>
      <div class="col-8 bg-warning">
      <p>Sed ut perspiciatis...</p>
    </div>
  </div>
 </div>
<!-- 50%/50% split -->
<div class="container-fluid">
  <div class="row">
      <div class="col-6 bg-success">
      <p>Lorem ipsum...</p>
    </div>
      <div class="col-6 bg-warning">
      <p>Sed ut perspiciatis...</p>
    </div>
  </div>
 </div>
Try it Yourself »Auto Layout Columns
In Bootstrap 4, there is an easy way to create equal width columns for all devices: just remove the number from .col-* and only use the .col class on a specified number of 
col elements. Bootstrap will recognize how many columns there are, and each column will get the same width:
  <!-- Two columns: 50% width-->
<div class="row">
  <div class="col">1 of 
  2</div>
 
<div class="col">2 of 2</div>
</div>
<!-- Four 
  columns: 25% width-->
<div class="row">
  <div class="col">1 of 4</div>
 
<div class="col">2 of 4</div>
  <div class="col">3 
  of 4</div>
  <div class="col">4 of 4</div>
  </div>
The next chapter shows how to add a different split percent for small devices.