Basis off Bootstrap 3 Bootstrap 4 Grid System It is based on 4 tier grid system (xs, sm, md, lg). It is based on 5 tier grid system (col, sm, md, lg, xl). CSS File LESS SASS Horizontal Form .row class is not required using grid in forms. .row class is required when using grid in form. Primary Unit px rem Font Size 14px 16px Responsive Image Use .img-responsive class. Use .img-fluid class. Image Alignment Use .pull-right and .pull-left class. You can use .pull-right, .pull-left Offsetting Columns Uses col-*-offset-* classes to offset columns. For example, col-md-offset-4. Uses offset-*-* classes to offset columns. For example, offset-md-4. Flexbox No Yes Generic Class No mt-1, pt-2