New to cycling

Hello everyone. Came accross this excellent site, after I purchased my first bike, so missed out on the great advice. Just wanted to share my story. I moved out to Malaysia from the UK and have been looking to getting into cycling for a while. My main problem out here has been trying to find a bike that fits. I decided on a road bike, and the largest frame I could find was a medium. I was confused by the bike size conventions used by manufacturers, seat post size, top tube size etc. One shop wanted to sell me a medium frame but it just didn't feel right. After a couple of weeks searching, I managed to track down a large Avanti Inc 2.0. The bike is also available in XL, but that would have meant a special order from New Zealand and an extra 300 pound delivery charge, bringing the price to 1200 pounds. So I tried the large (seat tube 475mm, top tube 575mm) and it seemed comfortable (I'm 6'1"😉. I managed to haggle the price down to 500 pounds. After a couple of weeks use, I don't seem to be suffering any aches and pains and the ride is fairly comfortable. My saddle is raised up to approximately (just under) the same height as the handlebars, and my resulting feet position is between flat and tiptoe. Just for future reference, what is the usual convention for bike sizing? Thanks