[The Glyphstone]

Lexicanum says a battlefleet is usually between 50 and 75 ships, up or down depending on the relative threat level. So it's only, at worst, a 6-1 margin without local support ships. Though I understand the Battle of Reach did have at least one Supercarrier there, so the largest Covenant ship in play will outclass the largest Imperial ship in play if they each get a full fleet to play with. The average Imperial ship size is far larger than the average Covenant ship size, though, even with a supercarrier dragging the median up - the Lunar cruiser's apparent opposite number is the 1.7km CCS Battlecruiser, and the smallest ship the Imperial Navy deploys are escort-class destroyers at 1.5km.