I keep hearing a repeating theme: small, 3" Screen
Grab your Pica stick and a mass market paperback.
Measure a line of text in a normal chapter (margin to Margin): 3.375" inches
If you don't Add extra
Margins (the device Bezel/mask, is the 'built in' margins).
That is not much difference in width from Billions of dead tree books sold here in the USA