The main cuttles that are kept as pets are Sepia bandensis and Sepia officinalis. Bandensis are relatively small. We used to think a 29 gallon tank was sufficient for them, but there have been a few cases where they seemed to get too big for that when fully grown. They are also the only cuttles currently easy to get as pets, since Thales and Paradox are breeding them (Shipposhack had some recently as well, and I think maybe someone else I can't remember just now) and others have bred them in the past. They can get a few inches long.
Officinalis are common in Europe, and get considerably larger, up to 18 inches, I think. They need a quite large tank, I think 200 gallons or larger, but maybe 125. They also do better in cylindrical tanks. Pharonis get a bit bigger still, but as far as I know have never been available in the pet trade, although a few of the professionals have kept them. The largest cuttles get to be 3 or 4 feet long, Sepia apama is the giant Australian variety, but I think there's one near Asia that gets a bit bigger. As far as I know, they haven't been kept in captivity, but you did ask "biggest."