The Mathematics of Masonry

Laying a brick wall involves surprisingly precise mathematics. Because bricks are rigid, standardized blocks, calculating the exact quantity required is a matter of calculating the surface area of the wall and dividing it by the surface area of a single brick. However, a major component that DIYers often overlook is the Mortar Joint.

If you stack bare bricks directly on top of each other, your math will be completely wrong. A wall is not just made of bricks; it is made of bricks suspended in a matrix of mortar. In the United States, a standard mortar joint is 3/8 of an inch thick. To calculate correctly, you must add that 3/8 inch to both the length and the height of every single brick to determine the "Effective Area" that each brick covers on the wall.

Why Are There So Many Brick Sizes?

Walking through a brickyard, you will see a bewildering array of sizes: Standard, Modular, Queen, King, Utility, etc. Why not just use one size?

• Modular Bricks: This is the most common size in commercial construction. They are mathematically designed so that exactly three horizontal courses (rows) of bricks, including their mortar joints, equal exactly 8 inches in height. This makes it incredibly easy for a mason to align the bricks with standard windows and doors.
• King and Queen Bricks: These are physically larger face bricks. Because they are larger, you need fewer of them to cover the same wall area. This reduces the amount of mortar required and speeds up the labor, making the overall wall cheaper to build.
• Utility Bricks: Massive bricks often used in commercial structures behind the scenes to build structural walls rapidly.

Estimating Mortar

Mortar is the adhesive that binds the bricks. It is not concrete. Mortar is made by mixing masonry cement (or Portland cement and lime) with fine sand and water. It contains no gravel, allowing it to spread smoothly like peanut butter.

Calculating mortar volume is difficult because it depends heavily on the skill of the mason. A messy mason will drop a significant amount of mortar on the ground, and striking (tooling) the joints deeply removes more material from the wall. As a general industry rule of thumb, you need roughly one cubic foot of wet mortar for every 50 to 60 standard bricks laid.