Field calculator
CMU block calculator (blocks and mortar)
Ordering for a block wall comes down to the wall area and the size of the unit. A standard 8 by 8 by 16 inch concrete masonry unit has a nominal 8 by 16 inch face once the mortar joint is included, which covers about 0.89 square feet, so a wall needs roughly 1.125 blocks per square foot. Enter the wall area, with door and window openings deducted, and a waste percentage for cuts and breakage. Mortar runs about one 80 pound bag for every 28 to 32 blocks, often stated as roughly three bags per hundred block. This calculator counts the blocks and the mortar; order grout, rebar, and horizontal joint reinforcement separately based on the reinforcement schedule, since grouted and reinforced walls need fill and steel the block count does not capture. Yields shift with the block size, the joint thickness, and the mortar type, so confirm the unit dimensions and the bag yield with your supplier before the order.
Result
CMU block and mortar count: a standard 8x8x16 inch concrete block has a nominal 8x16 inch face (with the mortar joint), which covers about 0.89 square feet, so a wall needs roughly 1.125 blocks per square foot. Enter the wall area and a waste percentage. Mortar runs about one 80 lb bag per 28 to 32 blocks (three bags per hundred is a common rule). Subtract door and window openings from the area, and order grout, rebar, and joint reinforcement separately. Yields vary by block size, joint thickness, and mortar type, so confirm the unit dimensions and bag yield with the supplier.
anvilfield.com/calculators/cmu-block-mortar-calculator · Free field calculators and FieldOS. A planning estimate, verify against the code, the manufacturer, and the engineer of record.
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CMU block FAQ
What mortar type should I use for a brick wall?
For most above-grade exterior brick and block, Type N mortar is the common choice. Use Type S at or below grade and where the wall sees more flexure, Type M below grade and on retaining walls, and Type O for interior or repointing soft, historic brick. Match the mortar to the unit and verify the specified type.
What is a cavity wall?
A cavity wall is two wythes of masonry with a deliberate air space between them. That air space is a drainage gap: water crossing the outer wythe runs down the back of the face, lands on flashing at the base, and exits through weeps. The backup carries a water-resistive barrier and, in many walls, the structural load.
Why do brick walls have weep holes?
Brick walls have weep holes because the wall collects water behind the face on flashing, and that water has to drain back out. The weep is the open path at the flashing line that lets it out. Without weeps the flashing fills like a bathtub, saturates the wall, and pushes water inside. Keep weeps open and above the flashing.
What is the difference between a control joint and an expansion joint in masonry?
A control joint is for CMU, which shrinks, so the joint opens and sends shrinkage cracks to a planned line. An expansion joint is for clay brick, which grows, so the joint is a compressible gap that closes as the brick expands. Control joints can take mortar; brick expansion joints never get mortar, only backer rod and sealant.
Should masonry mortar be stronger than the brick?
No. The mortar should be weaker than the unit so that movement cracks the joint, which you can repoint, instead of the brick, which you cannot. A mortar harder than the brick concentrates stress at the face and spalls the units. This rule governs restoration: hard portland mortar on soft historic brick destroys the wall.