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About Concrete Block Calculator
Calculate total CMU blocks, face-shell mortar bags, and core-fill grout volume needed for concrete masonry unit walls, retaining walls, and foundation stems.
Inputs and calculations stay in your browser and require no signup.
How the calculation works
Planning calculation
Net wall area = (length × height) − openings area; Exact CMU blocks = net area × 1.125 blocks/ft²; Purchase blocks = ceil(exact blocks × (1 + waste/100)); Mortar = purchase blocks × 0.135 ft³; Core grout = purchase blocks × cores/block × 0.33 ft³ / 27.
How to use this calculator
- 1Enter measured project dimensions and quantities.
- 2Adjust material, spacing, waste or density assumptions to match the project.
- 3Review the live planning quantities.
- 4Round purchasing quantities appropriately and confirm field conditions.
Understanding the result
Nominal 8x8x16 CMU blocks cover 1.125 blocks per square foot of wall face (0.8889 ft² each). Grouting schedules can be hollow (0 cores), 32" on-center (0.5 cores/block), 16" on-center (1 core/block), or solid grouted (2 cores/block).
Results use the units shown beside each field and output.
Important limitations
- Structural reinforcement spacing, bond beams, and vertical rebar cores must be designed by a licensed structural engineer.
- Opening takeoffs should account for lintel blocks, bond beams, and half-blocks at jamb corners.
- Core fill grout volume assumes standard 2-core hollow CMU units without excessive blow-outs.
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Frequently asked questions
How many concrete blocks are in a square foot of wall?
One standard 8x8x16 CMU block measures 15-5/8" × 7-5/8" plus a 3/8" mortar joint (16" × 8" nominal). This equals 128 square inches or 0.8889 sq ft, meaning you need exactly 1.125 blocks per square foot of wall surface.
How much grout does an 8-inch CMU block hold?
Each core cell in a standard 8x8x16 hollow CMU block holds approximately 0.33 cubic feet of grout. Filling both cores completely requires about 0.66 cubic feet per block.
What waste percentage should I order for concrete blocks?
A 5% to 10% waste allowance is standard for straight walls to account for cuts at corners, half-blocks, and transit breakage. Order 10% to 15% for complex walls with numerous window and door openings.
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