Granite worktops mainly come in two thicknesses 20mm or 30mm, however they are also available in 40mm thickness. But 40mm thick granite worktops are rare and normally cost twice the price of 30mm granite worktops and are not available in all colours. Most kitchens can not support 40mm thick granite worktops as they weigh a lot more than 30mm worktops and the extra weight can cause the kitchen units to collapse.
For your kitchen worktops I would always recommend 30mm granite worktops as they are stronger and more durable than 20mm worktops. Also 30mm granite worktops aesthetically look better than 20mm worktops as they look chunkier.
All upstands, splashbacks and windowcills are manufactured from 20mm granite for aesthetics. As they look better as they are not as thick as the worktops. Beware of companies who manufacture your upstands, splashbacks and windowcills in 30mm as they only do this as it is cheaper for them to cut them from the same slab as your worktops rather than from a 20mm slab. But they will not look as good as 20mm upstands, splashbacks or windowcills as they will project to far out from the wall and will be the same thickness as your worktops.
As many of our clients are often replacing their existing 40mm thick laminate worktops for granite worktops. Therefore if they go for standard 30mm thick granite worktops they would have to pack their worktops using 8mm ply or use upstands to hide the 10mm gap between the tiles and worktops. However not all customers want to pack up their worktops or go for upstands. Therefore we are able to offer more cost effective 40mm thick granite worktops by bonding two 20mm granite worktops together, giving the appearance of 40mm granite worktops. To combat the weight issue associated with solid 40mm thick granite worktops, we only use a strip of 20mm granite at the front. Therefore all kitchens are able to support these 20mm plus 20mm worktops.
Finally with 30mm granite worktops you do not have an issue with sink or hob cutouts being too weak as you do with 20mm worktops. As 30mm granite worktops are very strong and durable even lighter granite colours such as Kashmir White, Giallo Imperial and Azul Platino can support most sinks and hobs.