You are limited to 50 000 URLs or a 10 megabyte file. However, you can split your sitemaps across several files and submit a sitemap index that points to the individual files to Google. Overall you are limited to 500 sitemaps, so that's potentially 25 000 000 URLs.
You can read more details and examples about all sitemaps types including XML sitemaps if you interested. Some sitemappers include support for splitting into multiple sitemaps when necessary + creating a sitemap index file.
50K is all right, thanks everyone. Now, I must break the big xml files into several parts, in order to fill the Google.
Submit the XML feeds for Google, increase your index page(s) more and more easy, make more bigger and stronger with your site.