Calculate the number of concrete blocks needed for a project by determining the number of blocks to complete a row and the rows to reach the desired height. Standard blocks are 8 inches by 16 inches, including the mortar joints.
To determine the number of blocks per row, a mason first measures the length of a wall in feet. He rounds any measurements over an even foot to the next number and determines the number of blocks each row requires by multiplying the measurement by 0.75. He calculates the number of rows by multiplying the height of the wall by 1.5. The total number of blocks to complete the project is the product of the blocks in a row times the number of rows. Concrete block suppliers recommend adding 5 to 10 percent to account for breakage and errors.
Manufacturers state the size of the block using width by height by length, so a 6 x 8 x 16 concrete block has a face size of 8 inches high and 16 inches long with a 6-inch width. While the face size remains the same for most concrete blocks, thickness varies but does not affect the number of blocks needed. If using blocks with a nonstandard face size, the mason converts the factors by dividing both height and width by 12.