What is the largest screen size you generally code for?

I’m talking about just your general webpage/landing page/etc. In Firefox’s responsive design mode there are options for 720p/1080p, and even 4k televisions. Is it normal to make your webpage responsive in all of these sizes? How high do you normally go?

it depends - what target do you want to reach? and what are the most used devices (screen size) used by that target?

Once devices get over phone sizes, you don’t write for width/height in pixels, you write for aspect ratios. The 720p, 1080p, and 4k screens are all using 16:9 aspect ratios, so they’re really all the same as far as layout goes. It’s also reasonable for most sites to assume that’s as wide as a screen is reasonably going to get. And by assume, I just mean not going out of your way to support wider ratios than that. It should still be responsive at all kinds of aspect ratios though.

In order to properly support high definition displays though, you’ll want to always specify sizes in ems, rems, or percentages. Even for images. Especially for images. And also use scalable formats like SVG wherever possible. The reason FF has all those resolutions for the same aspect ratio is so you can see what happens to the layout if some parts are laid out in pixels and others are in relative units like ems/rems.