Here are the conversions for troop sizes. For more accurate information you will need to have Informantics higher and/or more scouts.

Range Few 1 - 24
Pack 25 - 49
Lots 50 - 99
Horde 100 - 249
Throng 250 - 499
Swarm 500 - 999
Zounds 1000-2499
Legion 2500 - 4999
Bulk 5000 - 9999