Which size suits how many scoops
The coupes here run from 18 to 38 cl, and that difference is bigger than it sounds. A coupe of 20 to 25 cl holds two to three scoops of ice cream plus a swirl of whipped cream: the classic size for a dame blanche or a sorbet after dinner. From 28 cl you are in sundae territory, with room for four scoops, sauce, fruit and cream without anything going over the rim. The models of 32 to 38 cl are ice cream parlour size and usually too generous for home.
Then look at the shape of the bowl. A rounded, bulging coupe collects meltwater at the bottom and keeps the ice cream on top dry. A clean, straight bowl looks more modern but lets the scoops slump apart sooner. For a banana split or a tall sundae, a higher, narrower ice cream glass works better than a wide coupe. And mind the thickness of the rim: hospitality models have a reinforced rim, because a coupe with a metal spoon in it spends the whole evening rattling on a tray.