Viewport breakpoints: desktop, tablet and mobile px sizes
We have established a viewport setting which manages devices with the following pixel sizes:
Desktop: from 1024px onwards
Tablet: from 768px to 1023px
Mobile: anything below 767px
So with this in mind, you can plan your template with exact pixel knowledge if needed.
For a full list of devices and their viewports you go to: http://viewportsizes.com/