Calculators/ Masonry & Aggregate/Concrete Block Calculator
Concrete Block Calculator
CMU block counts for a wall, plus mortar and fill.
A standard concrete block is nominally 8 by 16 inches on the face, including the mortar joint, which works out to exactly 1.125 blocks per square foot. That figure holds whether the block is 4, 8 or 12 inches thick, because only the face dimension changes coverage.
How this is calculated
- Net wall area = length × height, minus openings.
- Multiply by 1.125 blocks per square foot. This assumes standard 8 × 16 nominal face with a 3/8 inch joint.
- One 80 lb bag of mortar mix lays about 13 blocks.
- If cores are being grouted, each hollow block holds roughly 0.28 cubic feet. Reinforced walls usually fill only the cells containing rebar.
Frequently asked questions
How many blocks per square foot?
Exactly 1.125, because a nominal 8 by 16 inch face covers 128 square inches and there are 144 square inches in a square foot.
How many blocks in a course?
A nominal block is 16 inches long, so a course takes three quarters of a block per foot of wall. A 30 foot wall needs about 23 blocks per course.
Do I need to fill the block cores?
Not usually for a garden or non-structural wall. Retaining walls and load-bearing walls typically grout the cells that contain vertical rebar, which local code will specify.