http://www.dakkadakka.com/dakkaforum/posts/list/31.page JForum - http://www.jforum.net http://www.dakkadakka.com/dakkaforum/posts/preList/687745/8593172.page http://www.dakkadakka.com/dakkaforum/posts/preList/687745/8593172.page GMT http://vignette3.wikia.nocookie.net/warhammer40k/images/3/38/Space_Marine_Legion_Structure_1.jpg/revision/latest?cb=20131001033403

In practice it was a random mess, partly due to the character of each legion, partly because Black Library authors can't be bothered with boring things like TO&E when they can just throw around large numbers and words like Great and Grand. ]]> http://www.dakkadakka.com/dakkaforum/posts/preList/687745/8593398.page http://www.dakkadakka.com/dakkaforum/posts/preList/687745/8593398.page GMT
10 squads - 1 company
10 companies - 1 chapter
10 chapters - 1 legion

obviously some of them were much bigger or had different organisation patterns but that's the basic way I have always pictured it in my head.]]> http://www.dakkadakka.com/dakkaforum/posts/preList/687745/8602437.page http://www.dakkadakka.com/dakkaforum/posts/preList/687745/8602437.page GMT
IIRC, the Death Guard only had 7 'Great Companies', with Nathaniel Garro the 'Battle Captain' of the 7th Company. I can't remember their supposed numbers, though.]]> http://www.dakkadakka.com/dakkaforum/posts/preList/687745/8602493.page http://www.dakkadakka.com/dakkaforum/posts/preList/687745/8602493.page GMT
I guess the easy answer to your question is: there is no legitimate answer unless you are asking about a specific legion.]]> http://www.dakkadakka.com/dakkaforum/posts/preList/687745/8602881.page http://www.dakkadakka.com/dakkaforum/posts/preList/687745/8602881.page GMT http://www.dakkadakka.com/dakkaforum/posts/preList/687745/8602938.page http://www.dakkadakka.com/dakkaforum/posts/preList/687745/8602938.page GMT