Resolution vs print size

Is there any kind of standard for resolution = print size. I think I am going to make a website and try and sell a few photos of wildlife. I have to crop some photos, so after a crop, I may not be able to print off a large print. I am trying to figure out some kind of standard so I can set maximum print size for my photos. If you have info or a link pointing me in the right direction I would greatly appreciate it.

Optimal print resolution depends on your print size and viewing distance (the shorter your viewing distance, and the larger your image, the more resolution your image should have). Websites don't have to have such high resolutions (and images are optimized better if there's little to no scaling). If you're making a website, I would make images that are web sizes, and then have links to larger full size print versions. Services like smugmug are pretty good for organizing image libraries, and providing links to resized images for linking on websites.

The way I have it set up now. People would view the photo which is resized for web friendly and if they want it they would purchase it and I will get the info on the print they want and size and send that off to the printers. So I want to no how large a print I can make based on the resolution of the image.

Generally I go 300 PPI (pixels per inch) on my prints. Take the dimensions of the file and divide each side by 300, that would give you the approximate print size. But the 300 ppi will change based on how far away you expect your audience to be from the print. The further away from the print you expect people to be, the lower the ppi has to be.