For years, the sitemaps protocol defined at www.sitemaps.org
stated that each sitemap file (or each sitemap index file) may contain no more than 50,000 URLs and must not be larger than 10MB (10,485,760 bytes). While most sitemaps are under this 10 MB file limit, these days, our systems occasionally encounter sitemaps exceeding this limit. Most often this is caused when sitemap files list very long URLs or if they have attributes listing long extra URLs (as alternate language URLs, Image URLs, etc), which inflates the size of the sitemap file.
To address these evolving needs, we are happy to announce that we are increasing sitemaps file and index size from 10 MB to 50MB (52,428,800 bytes). Webmasters can still compress their Sitemap files using gzip to reduce file size based on the bandwidth requirement; however, each sitemap file once uncompressed must still be no larger than 50MB. The update file size change is now reflected in the sitemap protocols on www.sitemaps.org
This update only impacts the file size; each sitemap file and index file still cannot exceed the maximum of 50,000 URLs (<loc> attributes).
Having sitemaps updated daily, listing all and only relevant URLs is key to webmaster SEO success. To help you, please find our most recent sitemaps blog posts
· Sitemaps Best Practices Including Large Web Sites
· Sitemaps – 4 Basics to Get You Started
Principal Program Manager
Microsoft - Bing