Wetsuits generally work as below, there are some such as Rip Curl, who as a 5/3 will have 5 over the core and legs and 3 on the shoulders and arms.
5/4 5mm on the core and 4 elsewhere (Winter Suit)
4/3 4mm on the core on 3 elsewhere (Year-round suit)
3/2 3mm on the core and 2 elsewhere (Spring / Summer suit)