Desktop Illustrator documents are 1680px wide:
240px margin · 1200px contents · 240px margin
Illustrator gridline every 240px · 24 subdivisions
Mobile Illustrator documents are ¼ as wide, 420px wide:
60px margin · 300px contents · 60px margin
Illustrator gridline every 60px · 4 subdivisions
These sizes ensure that 13px text translates to legible text on the screen.
The gridline settings make it easy to know which content is within the margins.