Concrete Block Calculator
Blocks and mortar for CMU walls — 8×8×16 runs 1.125 blocks per square foot, and this page shows you why, then does it for the half-height and half-length variants too.
Core fill and rebar in a structural wall are an engineering call, not a calculator call — this line only counts grout volume for a fill you have already decided on.
The 1.125-per-sq-ft figure is the industry nominal count for 8 × 16 faces with a standard joint — the same number the block yard uses. Mortar is figured at about 12 standard blocks per 80 lb bag of mortar mix.
How the math works
A standard 8×8×16 block with a ⅜″ joint covers 8.375″ × 16.375″ of wall — 0.889 sq ft nominal, which the industry rounds to the clean planning figure of 1.125 blocks per sq ft. This page uses that standard figure (it matches how suppliers and estimating tables count) rather than the raw joint math, and says so. Half-height (4″) and half-length (8″) units cover half the face, so they run 2.25 per sq ft.
Mortar at about 12 standard blocks per 80 lb bag of premix. The optional core-fill line figures grout at roughly 1 cubic yard per 120 standard blocks with every core filled — real grout volume depends on bond beams, vertical steel spacing, and how many cells the plans actually call filled, which is an engineering call, not a calculator call. Count the units here; let the plans say which cores fill.
A worked example
A 20 ft × 8 ft standard block wall: 160 sq ft × 1.125 = 180 blocks exact, 198 to buy at 10% waste — and 198 ÷ 12 = 17 bags of mortar (16.5, rounded up, because a half-bag is a second trip). With every core filled it would also want about 1.65 yards of grout; flip the core-fill option on above and check.
Questions from the field
How many concrete blocks per square foot? 1.125 for standard 8×8×16 block — the figure the whole industry counts with. A 100 sq ft wall is 113 blocks exact, about 124 with waste.
How many blocks do I need for a 20 × 8 wall? 180 on paper, 198 with a 10% waste factor. Waste on block covers cuts, breakage, and the corner and jamb units the simple count smooths over.
How much mortar for 100 blocks? About 9 bags of 80 lb premix at 12 blocks per bag (100 ÷ 12 = 8.3, buy 9). The mortar calculator figures bags from any unit count, both bag sizes.
How much grout fills block cores? About 1 cubic yard per 120 standard blocks with all cores filled. Bond beams and partially filled walls change it — fill volume follows the structural plans, never a web calculator.
The other masonry calculators
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