For best readability on most devices, use a 16pt font. (Since mobile devices are typically held closer to the eyes, drop down to 14pt for small screens.) If you're on a wide screen device, resize your window to see for yourself.
When line lengths get past 600-700px, they start getting harder to read. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nunc eget turpis diam. Duis sagittis viverra dolor vel sodales. Sed sit amet bibendum erat, et hendrerit tellus. Suspendisse venenatis orci vitae nisi vulputate bibendum. Nam erat orci, vulputate id augue quis, luctus pharetra tortor. Maecenas consequat erat mi, porta varius mauris sollicitudin et. Ut feugiat semper sodales. Nam ut magna faucibus, auctor nibh ac, laoreet odio. Sed eu lorem ut mauris vehicula sodales. Ut ipsum ante, hendrerit eu mattis ac, feugiat in dolor.
On a 1200w laptop screen, they're downright obnoxious. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nunc eget turpis diam. Duis sagittis viverra dolor vel sodales. Sed sit amet bibendum erat, et hendrerit tellus. Suspendisse venenatis orci vitae nisi vulputate bibendum. Nam erat orci, vulputate id augue quis, luctus pharetra tortor. Maecenas consequat erat mi, porta varius mauris sollicitudin et. Ut feugiat semper sodales. Nam ut magna faucibus, auctor nibh ac, laoreet odio. Sed eu lorem ut mauris vehicula sodales. Ut ipsum ante, hendrerit eu mattis ac, feugiat in dolor.
What this means for web design is that there’s a maximum usable width for your main content column. If you’re aiming to use a single layout across all breakpoints, that means there’s a maximum usable width for your site and it’s about the size of an iPad.