Definitions of breakpoints

First off I’d stop think of things as mobile, tablet and desktop. The latest iPads use a Mac user agent, and some are as large as a small laptop. Some folks phones are as big as other tablets.

That can vary from theme to theme (or framework to framework) and stack to stack.

For example, the RapidWeaver 8 themes that come with RW Artful, Climate, Enginer, Future and Mountains are all based on Bootstrap 4. Also all the ThemeFlood themes use Bootstrap 4 breakpoints:

Size Breakpoint
Small min-width:576px
Medium min-width:768px
Large min-width:992px
Extra Large min-width:1200px

Now the standard breakpoints for the stacks that come with stacksand the point at where the "Hide This Stack happen are as follows:

Size Breakpoint
Mobile max-width: 440px
Tablet (max-width: 770px) and (min-width: 441px)
Desktop min-width: 771px

And Frameworks and 3rd party stacks can vary.