Don't try to measure the squares on your screen. It's impossible for an artist to know the viewer's screen resolution and size, so there's just no sense in measuring it that way. For instance, my monitor, at its native resolution of 1920 x 1080, is 101 ppi.

Anyway, 1400 pixels / approximately 27 squares means that the squares are ~50 pixels. So if you print at 50 dpi, you'll get approximately 1" squares.