Stone-work is estimated by the perch; 24 3/4 cubic feet making one perch. An 18-inch wall, 1 foot high, and 16 1/2 feet long, contains one perch.

Brick-work. - Bricks are usually estimated at 25 to the cubic foot. They usually lay 5 courses to each foot in height.

For an 8-inch wall, allow 17 bricks for each square foot of surface. For a 12-inch wall, allow 25 bricks for each square foot of surface. For a 16-inch wall, allow 34 bricks for each square foot of surface.