Concrete blocks are commonly referred to by their nominal sizes. A block totaling 9 5/8 inches wide is referred to as a 10-inch block because a standard 3/8-inch mortar joint will increase the total width for the course to 10 inches. Concrete blocks are available in both solid and hollow configurations. The American Society for Testing and Materials defines a hollow concrete block as one where the cores of the block account for over 25 percent of the total cross-sectional area.
A 6 x 8 x 8-inch sash block has a single rectangular core measuring 35/8 inches wide by 4 7/8 inches. The corners of a 6 x 8 x 8-inch sash block are rounded at a 5/8-inch radius. A 6 x 8 x 14-inch concrete pier block has two cores, both measuring 3 5/8 inches wide by 5 5/16 inches long. The two hollow cores on a 6 x 8 x 16-inch pier block are 7 5/16 inches long and identical in width to the cores on a 6 x 8 x 14-inch block.
An 8 x 4 x 16-inch double stretcher block has two hollow cores measuring 5 1/8 inches wide by 5 9/16 inches long. The two large hollow cores on an 8 x 4 inch x 16-inch split pier block both measure 5 1/8 inches wide by 5 3/8 inches long. The 8-inch pier blocks also have a small central core measuring 5 1/8 inches long by 3/8 inches wide. An 8-inch square sash block has a single, slightly offset hollow core measuring 4 3/8 x 5 1/8-inch long; 8 x 8 x 12-inch hollow blocks have two cores measuring 4 1/16 inch wide by 5 1//8 inches long.
A 10 x 8 x 16-inch pier block has two equal cores measuring 6 1/16 inches wide by 7 1/8 inches long. The two cores in a 10 x 8 x 16-inch "L" corner block measure 5 1/8 inches wide by 5 11/16 long. A 10 x 8 x 16-inch sash block has three total cores. The small central core measures 38 inches wide by 7 1/8 inch long while the two larger outer cores measure 4 5/8 inches wide by 7 1/8 inches long.
A 12 x 12 x 8-inch sash block has a single, slightly offset core measuring 4 4/16 inches wide by 8 5/8 inches long. In addition to the hollow core, a 12-inch sash block also has a 3/4 inch square notch running up the entire height of a long-sided face. The notch is located 7 7/16 inches from the left side of the block. A 12 x 8 x 12-inch pier block has two equal hollow cores measuring 7 3/4 inches wide by 8 5/8 inches long.