This is what I do when I'm stuck on the toilet in a public bathroom. I estimate the dimensions of the tiles on the floor, usually 4,6 or 12 inches. I use this number to estimate the length and width of the stall. If I'm sitting in the stall next to the wall, I do the same thing with the tiles on the wall and calculate the square footage of the walls and front and back sides of the stall. If there are no tiles on the wall, I just estimate them. I take those numbers and figure the volume and surface area of the stall in cubic or square inches, feet and yards.If I'm still in the bath room after all of that, I might figure out how many gallons that is. If that isn't enough, I look at the patterns in the tile or the bumps on the ceiling to see if there are any hidden images. Hopefully by that time, I won't be in the bathroom anymore.