[Vince]

This formula can be used to work out the revised area: –
(ceiling(Width / 4) * 4) * (ceiling(Height / 2) * 2)

However, this relies on the markup being the correct orientation and also being a rectangle or square.

If the room is an irregular shape, then I can only see using a template grid as being the way to work out exactly how many whole tiles are required.

Edit: – You could also add “/8” at the end of the above formula to get the number of whole tiles..