Example is shown is in door style C. Hand painted in Bone by Farrow & Ball
This is a full Mantel.
Each side is 320mm - 400mm wide.
Inside can be inset by 6mm to allow for tiling.
Underside is inset 20mm to allow for an integrated extractor.
Also make sure that you check your hob manual (or website) to get the minimum height from hob to extractor. As a guide it is likely to be about 650mm for an electric hob or 760mm for a gas hob, but you MUST install according to your hob manufacturers instructions!