How big can a African snail grow up to?

It depends on the species of snail. The weight of different species can vary greatly. Here are the weight ranges of a few common snails:

Helix pomatia, or edible snail - size: 40 to 55 mm for an adult weight of 25 to 45 g.

Helix aspersa also known as the European brown snail- size: 28 to 35 mm for an adult weight of 7 to 15 g.

Helix aspersa maxima - size 40 to 45 mm for an average weight of 20 to 30 g.