Our WarmBoards tile backer insulation boards are paticulary suited to under-tile heating, these are a must for anyone who wants primary heating. Insulating on top of an existing un-insulated concrete or timber floor will greatley reduce warm up times, running costs and maximise's the use of the cables. All WarmBoards are 1200mm x 600mm = 0.72m² To work out how many you need, simply divide your floor area by 0.72m², then round it up to get the number of boards you need, and don_t forget you will need a level floor to tile on to, so for example if you have a room that you are tiling wall to wall but only putting heating in the center, then you will need enough boards to go wall to wall to give you a level floor and not to cover only the central heated section. If you need any help just email or phone us and ask.