Well, over here in the US one of the most popular size coolers for sous vide is. as you probably already know, the Coleman 24 can Party Stacker. It's interior dimensions are: 16.375 in. (41.6 cm) x 11.125 in. (28.3 cm) x 6 in. (15.2 cm).
I think this probably gives you a maximum cooking volume of 16 liters as you wouldn't want it filled too close to the top!
The thing I like about the Coleman 24 can is that when I clamp the Anova on the side it rests perfectly on the bottom, as if it were made for it!
I hope the above info helps!