Some mobile device dimentions: Nexus 5 360 598 Nexus 6 412 690 iPhone 5 320 568 iPhone 6 375 667 iPhone 6+ 414 736 Galaxy 5 360 640 Galaxy 6 360 640 iPad 768 1024 Galaxy 2,3 10" 800 1280 Galaxy 2 7" 600 1024 Based on this, we define the following size brackets: 320-359 small phone portrait 360-567 big phone portrate 568-1023 phone landscape, tablets portrate 1024- tablets landscape, monitor Body min-width: 320px ~ 20em @ 16px font-size. This is factored in when doing font boosting. Specifying 320px directly seems to mess it up. Font boosting results for font-size:1.1em (~18px), min-width:18em on Nexus 5: - about 40 characters in portrait - about 70 characters in landscape - landscape font appears slightly smaller 18em on smaller phones (e.g., iPhone 4) appears to trigger scrolling. 17em works well, however.