How to Use the Masonry Mortar Volume Calculator
Before ordering material for a CMU (concrete masonry unit) wall, knowing how many blocks and how much mortar you'll need helps you avoid costly over- or under-ordering. This calculator uses the standard 8x8x16 in nominal CMU (actual size 7.625x7.625x15.625 in) to compute both figures from your wall area.
The calculation divides the wall area by the coursing area of one block, including the mortar joint, to get the block count, then subtracts the total block volume from the wall volume to get the mortar volume. With a standard 3/8 in (0.375 in) joint, this works out to the well-known industry rule of about 1.125 blocks per square foot of wall.
Real-world jobs always have some breakage, cutting waste, and mortar spillage, so it's standard practice to add a buffer on top of the calculated quantities — typically 3-5% extra blocks and about 10% extra mortar. Actual material needs can vary with wall detailing and site conditions, so confirm final quantities with your mason or a construction estimator before placing a bulk order.
Frequently Asked Questions
A common allowance is 3-5% extra blocks for breakage and cutting, and about 10% extra mortar for spillage and mixing loss.
A thicker joint reduces the number of blocks needed but increases mortar volume. Standard 8x8x16 CMU construction typically uses a 3/8 inch (0.375 in) mortar joint.