Concrete Block Wall Calculator
Enter the wall length and height and this calculator returns the block count with NCMA's 5% waste allowance, the bags of mortar for the units you are laying, and the grout volume for the cell spacing you enter. Reinforcement is counted, never specified: bar size and spacing come from your drawings.
Blocks to order
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Results are estimates for planning purposes. Verify with your supplier, engineer, or a qualified professional before ordering material or performing work.
Units, mortar and grout per 100 square feet
| Unit type | Nominal face | Units per 100 ft² | Face area of one unit |
|---|---|---|---|
| Conventional | 8 × 16 in | 119 | 8/9 ft² |
| Half-high | 4 × 16 in | 238 | 4/9 ft² |
| Half-length | 8 × 8 in | 238 | 4/9 ft² |
| Brick-sized | 2⅔ × 8 in | 710 | 4/27 ft² |
NCMA TEK 4-2A Table 1, based on the net area of the wall and including about 5% waste and breakage. The count is independent of the unit width, so a 12 in wall takes the same number of blocks as a 6 in wall of the same face size.
How many units one batch of mortar lays
| Mortar | Conventional CMU | Brick-sized CMU |
|---|---|---|
| 70 lb bag masonry cement + 1/8 ton sand | 30 | 1,000 |
| 80 lb bag preblended mortar | 16 | 50 |
| 3,000 lb bulk bag preblended mortar | 420 | 1,550 |
| 80 lb bag QUIKRETE Mason Mix (Type S) | 13 | 37 standard bricks |
First three rows: NCMA TEK 4-2A Table 2, face shell bedding for conventional units and full bedding for brick-sized units, nominal waste included. Last row: QUIKRETE Mason Mix No. 1136 data sheet (5 quarts of water per 80 lb bag, 7 quarts maximum). NCMA publishes yields for conventional and brick-sized units only — for half-high and half-length units this calculator applies the conventional per-unit rate, which is deliberately generous, since a half unit uses less mortar than a full one.
Grout volume by wall width and grout spacing
| Grout spacing | 6 in wall | 8 in wall | 10 in wall | 12 in wall | 14 in wall |
|---|---|---|---|---|---|
| 8 in (every cell) | 25.6 | 36.1 | 47.0 | 58.9 | 74.5 |
| 16 in | 12.8 | 18.1 | 23.5 | 29.5 | 37.3 |
| 24 in | 8.6 | 12.1 | 15.7 | 19.7 | 24.8 |
| 32 in | 6.4 | 9.1 | 11.8 | 14.8 | 18.6 |
| 48 in | 4.3 | 6.1 | 7.9 | 9.9 | 12.4 |
| 72 in | 2.9 | 4.1 | 5.3 | 6.6 | 8.3 |
| 96 in | 2.2 | 3.1 | 4.0 | 5.0 | 6.2 |
| 120 in | 1.8 | 2.5 | 3.2 | 4.0 | 4.9 |
Cubic feet of grout per 100 ft² of wall — NCMA TEK 4-2A Table 3, two-core hollow units, 3% waste included. The full table also lists 40, 56, 64, 80, 88, 104 and 112 in spacings, all available in the selector above. NCMA does not recommend grouting conventional 4 in units: the cells are too small to consolidate.
Before you order
- Nominal is not actual. An 8 × 8 × 16 in block is 7⅝ × 7⅝ × 15⅝ in out of the pallet; the ⅜ in mortar joint makes up the difference. That is why the area math works on nominal dimensions.
- Corners, pilasters and bond beams are counted separately. NCMA is explicit about it: figure those units on their own and subtract them from the total, and deduct the area of every opening before you start.
- Non-modular layouts cost you. A wall length that is not a multiple of 16 in means cut blocks. NCMA warns that returns, corners and non-modular layouts can raise both the unit count and the mortar volume well beyond the table values.
- Bond beams need grout too. Table 3 covers vertical cells only. For horizontally grouted courses, NCMA's Table 5 gives about 2.0 linear ft of 8 in bond beam per 80 lb bag of preblended grout.
- Reinforcement is not our call. This tool counts vertical bars at the spacing you enter. Bar size, spacing, lap length, cover and grout strength come from your drawings or your engineer.
How it's calculated
- Net wall area
A (ft²) = length (ft) × height (ft) − openings (ft²)- Units to order
units = ceiling( A / unit face area × 1.05 )Unit face area is the nominal face: 8/9 ft² for a conventional 8 × 16 in unit, 4/9 ft² for a half-high or half-length unit, 4/27 ft² for a brick-sized unit. The 1.05 factor is NCMA's 5% allowance for waste and breakage, which is what produces the published 119 units per 100 ft² of wall.- Courses
courses = height (in) / nominal unit height (in)- Mortar bags
bags = ceiling( units laid / units per bag )Units laid per batch, face shell bedding for conventional units and full bedding for brick-sized units: 30 conventional or 1,000 brick-sized per 70 lb bag of masonry cement (with 1 ton of sand per 8 bags); 16 or 50 per 80 lb preblended bag; 420 or 1,550 per 3,000 lb bulk bag. QUIKRETE Mason Mix publishes 13 conventional blocks or 37 standard bricks per 80 lb bag. These yields already include a nominal waste allowance.- Sand for site-mixed mortar
sand (tons) = units laid / 240 ; 1 ton damp loose sand = 25 ft³NCMA: 1 ton of masonry sand per 8 bags of masonry cement, about 240 conventional units per ton. Above 3 tons, add half a ton for waste.- Grout volume
grout (ft³) = A / 100 × table value for wall width and grout spacingTable values are NCMA TEK 4-2A Table 3, ft³ per 100 ft² of wall, for two-core hollow units, including 3% waste. Example: an 8 in wall grouted every 32 in takes 9.1 ft³ per 100 ft². 4 in units are not in the table — NCMA does not recommend grouting them.- Grout bags
bags = ceiling( grout ft³ / 0.66 ft³ per 80 lb bag )An 80 lb bag of preblended grout yields about 0.66 ft³ and fills 3.6 cores of a 6 in unit, 2.7 of an 8 in, 2.2 of a 10 in or 1.8 of a 12 in unit. A 3,000 lb bulk bag yields about 25 ft³.- Vertical bars at your spacing
bars = floor( length (in) / bar spacing (in) ) + 1 ; linear ft = bars × height (ft)Count only. Bar size, spacing, lap length and cover come from your drawings or your engineer — this tool never suggests them.
Frequently asked questions
About 119 conventional 8 × 16 in blocks, per NCMA TEK 4-2A Table 1. The math: one unit covers 8/9 ft² of wall, so 112.5 units cover 100 ft², and NCMA adds 5% for waste and breakage. Half-high 4 × 16 in or half-length 8 × 8 in units run 238 per 100 ft², and brick-sized units 710.
It depends on the mix. NCMA gives 30 conventional blocks per 70 lb bag of masonry cement mixed with sand, and 16 per 80 lb bag of preblended mortar. QUIKRETE publishes 13 blocks per 80 lb bag of Mason Mix. All of these assume face shell bedding and include a nominal waste allowance.
Per NCMA TEK 4-2A Table 3, an 8 in wall takes 36.1 ft³ of grout per 100 ft² if every cell is filled (8 in spacing), 18.1 ft³ at 16 in spacing, 12.1 ft³ at 24 in and 9.1 ft³ at 32 in. Those figures are for two-core units and include 3% waste.
Twelve courses of conventional block: the nominal height of a standard unit is 8 in, so 96 in of wall height divided by 8 in gives 12 courses. Half-high units double that to 24.
NCMA works from one ton of masonry sand per 8 bags of masonry cement, which is roughly 240 conventional units per ton. A ton of damp loose sand is about 25 ft³. If the job takes more than 3 tons, NCMA says add half a ton for waste.
No, and no calculator should. It counts the vertical bars at the spacing you enter and gives the linear footage so you can price and order steel. Bar size, spacing, lap splices and cover are engineering decisions that belong to your drawings or your engineer.
Because of the 5% waste and breakage allowance NCMA builds into its estimating tables. Blocks get chipped, cut short and dropped. The calculator shows both figures: the net count and the count to order.
Sources & references
- NCMA TEK 4-2A — Estimating Concrete Masonry Materials (2004), Tables 1 to 5: units per 100 ft², mortar yields per batch, grout volume by wall width and grout spacing, preblended grout yields — Published by the National Concrete Masonry Association, now the Concrete Masonry & Hardscapes Association (CMHA).
- QUIKRETE Mason Mix (Type S Mortar) No. 1136 — product data sheet, revised November 2020: 13 standard 8 × 8 × 16 blocks or 37 standard bricks per 80 lb bag, 5 qt of water per bag
- Brick Industry Association — Technical Notes 10, Dimensioning and Estimating Brick Masonry (February 2009): nominal vs specified dimensions, brick and mortar quantities, waste allowances
Content checked against these sources — last reviewed August 29, 2026.