First measure the length and width of the room. Then deduct off any areas where the mat is not required E.g. under kitchen unit, vanity units, snooker tables etc. Then deduct off a further 15%.

So, if you have a conservatory that measures 3mtr x 3mtr. The calculation would be 3m x 3m = 9mtr2 less 15% = 7.65mtr2, then round up or down to the nearest mtr2. So you would need to order a 8mtr2 mat.