I think 7 ships were lost at Vulcan.
In TOS the size of the fleet was never covered apart from the existence of the 12 Connie's.
The fleet in TNG was substantial though, numbering likely hundreds and probably over a thousand starships (based mostly on the material from DS9). If you felt bold enough there's a long buried thread where Saquist and I debated (sometimes with others) and then argued over how big the fleet was during the time of the Dominion War. I have absolutely no idea where it is though. Probably way back in the DS9 subsection.
'If the Apocalypse starts, beep me!' - Buffy Summers
'The sky's the limit.....' Jean-Luc Picard, 'All Good Things'
courtesy of Saquist