Boostrap - .col-xm, .col-sm, .col-md, .col-lg, .col-xl Property and screen resultion

.col-xs extreme small size - mobile size <=544px
.col-sm Small size - Smartphone sise >=768px
.col-md Medium size- Avg Desktop size >=992px
.col-lg Large size - Bigger Desktop screen resolution >=1200px
.col-xl Extra Large size - Largest (TV) Screen >=1280px

<class=".col-xm-12" > is usual screen width implementation. 

Extra small <544px	Small ≥544px	Medium ≥768px	Large ≥992px	Extra large ≥1200px
Grid behavior	Horizontal at all times	Collapsed to start, horizontal above breakpoints
Container width	None (auto)	576px	720px	940px	1140px
Class prefix	.col-xs-	.col-sm-	.col-md-	.col-lg-	.col-xl-
# of columns	12
Gutter width	1.875rem / 30px (15px on each side of a column)
Nestable	Yes
Offsets	Yes
Column ordering	Yes