This is all an estimate, but assuming that the shower is a little over 10 tiles across (with each tile being 6" long), then I would say that it is 5' across. I would also assume that it is square, so it is probably 5' across on both sides. It is hard to tell from the photo, but it looks like the shower is 33 tiles tall. With each tile being 3" tall, then I would assume that the shower is about 8'3" tall.
16 months ago