You might find this useful:

http://www.mydevice.io/devices/

As has been said, physical size is not so important. I have a 15" laptop with a screen width of 2,880 pixels, but the browser sees it as 1440 pixels wide. My wife's laptop is 1,200 pixels wide and is a typical size for a screen.

960 pixels width is a safe size for desktops and most tablets in landscape orientation.

480 pixels wide is OK for phones in landscape orientation, but too wide for portrait.

320 pixels is the sweet spot for portrait orientation on phones.

Don't make your buttons too small.