Concrete Block Calculator
Blocks and mortar bags for your CMU wall — counted from the wall face, not guessed.
Your wall
Materials list
Generated by AllUnits.io — allunits.io/calculators/concrete-block
How this calculator figures it
Block count uses the standard estimating density of 1⅛ blocks per square foot of wall for 8×8×16 units laid with 3/8-inch mortar joints. Mortar coverage comes from the Quikrete Mortar Mix technical data sheet (TDS #1102): one 80 lb bag lays up to 13 standard blocks. Site-mixed masonry cement follows different coverage — use the data sheet for the product you buy.
How it works
Worked example — a 20 × 4 ft wall in standard 8×8×16 block: 80 sq ft × 1.125 × 1.05 waste = 95 blocks, and 95 ÷ 13 rounds up to 8 bags of 80 lb pre-blended mortar mix. Half blocks (8×8×8) run 2.25 per square foot with the same mortar rule per block.
Concrete block FAQs
How many blocks per square foot?
1.125 — an 8×16 face is 0.89 sq ft.
How many blocks does a bag of mortar lay?
Pre-blended 80 lb mortar mix: up to ~13 standard blocks per Quikrete's data sheet. The old "3 bags per 100 blocks" rule applies to site-mixed masonry cement plus sand — different product.
Type N or Type S mortar?
N for general above-grade, S for structural and below-grade — general practice, follow your plan/spec.
Do I need to fill the cores?
Only where the design calls for grout/rebar; core-fill volume varies by block — roughly 0.25 cu ft per standard block is a typical figure, confirm with your block supplier. Not calculated here.
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Related calculators & sources
Footing under the wall: Concrete Slab Calculator. Retaining soil instead: Retaining Wall Calculator. Framing above: Wall Framing Calculator. Mortar coverage is cited at Quikrete product data; convert measurements with the area converter.
Estimates for planning and purchasing. Not engineering or code-compliance advice — confirm structural work with your local building department.