1. Five Doors is Quite a Few
The ST has the same-size cargo area as the regular Fiesta hatchback; sort of. Official hatchback ratings are shrunk down to 10.1 cubic feet in the ST compared to 14.9 in the regular Fiesta five-door. Normal models have storage bins below the cargo floor, but the ST model comes with a full-size spare tire that eats up space. From the cargo floor to the roof, nothing is different dimensionally between the two Fiesta hatches.
Making things even more confusing, Ford officially rates the ST as having the same 25.4 cubic feet of total cargo volume that the non-ST hatchback does when the rear seats are folded. Regardless of the numbers, we were able to fit a pre-built vanity into the cargo-hold if the ST without issue. Try that in your FR-S.