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.