As of 1794, which Surprise most emphatically predates, as Aubrey served in her whilst a mid, the smallest frigates were 28 gun vessels, according to "The Frigates," James Henderson, CBE. Vessels of 20 and 24 guns were rated as post ships and were often sloops of war with a couple of guns added so that they were worthy of the dignity of a posted captain.

The actual number of guns, as mentioned above, does not truly relate to the rating. A 28 gun frigate, such as Surprise, had 28 guns on the main gun deck. The other guns were not counted in the rating.