Concrete Block Calculator: Blocks, Mortar & Grout
Enter a wall and get the blocks, the mortar bags as a sourced range, the core grout by cell spacing, and what an 8-inch wall weighs by density class.
By Marko VisicBSc Physics, University of Ljubljana
378blocks
8 in block, 5% extra included
1.125 per sq ft of wall
Mortar, grout and weight
- Mortar bags (80 lb premixed, CMHA 16 to Sakrete 12 blocks a bag)
- 24–32
- Grout, core fill
- none
- Wall weight at 31 lb/ft² (115 lb/ft³ units, CMHA)
- 9,920 lb
- Wall area, openings taken off
- 320 sq ft
Specified block width is 7.625 in.
Next: how much a block weighs, switch to brick, or size a concrete footing.
378 blocks for 320 sq ft of wall
A 40 by 8 ft wall is 320 square feet, so at 1.125 blocks per square foot it takes 360 standard blocks, or about 378 blocks once you add the 5% waste CMHA estimates with. An 80-lb bag of premixed mortar lays 12 to 16 blocks, so plan on 24 to 32 bags.
This is a calculator for a block wall of any size. For what a block or a grouted wall weighs, see how much a concrete block weighs; to estimate the whole job, see estimating a concrete project.
Estimate only: counts and mortar follow CMHA and manufacturer figures and vary with the block, joint and waste. Confirm quantities with your supplier before ordering.
How many blocks per square foot?
A nominal 8x16 block, with its mortar joints, takes up 8/9 of a square foot of wall. Turn that over and a wall needs 1.125 blocks per square foot, which the US Army's FM 5-428 prints as 112.5 per hundred square feet. CMHA's estimating figure, with a 5% waste allowance built in, is 119 per hundred square feet.
Block sizes: nominal versus specified
Block is named by its nominal size, which includes the mortar joint. The specified size you actually lay is 3/8 inch smaller each way, so an 8-inch block is really 7.625 inches wide. Nominal widths run from 4 to 12 inches and up.
Mortar for a block wall
The published yields disagree, so the calculator shows a range. An 80-lb bag of premixed mortar lays 12 blocks (Sakrete), 13 (QUIKRETE) or 16 (CMHA).
Mixed from scratch, a 70-lb bag of masonry cement with sand lays about 30 hollow units (CMHA, roughly 240 units per ton of sand), while QUIKRETE puts a 70-lb bag plus 240 lb of sand at about 46 standard blocks. Pick the mortar type in the calculator and it counts the bags.
Block fill: grout by cell spacing
Reinforced walls fill some or all of the cores with grout. The volume comes from the CMHA table of cubic feet per hundred square feet, by wall width and cell spacing, with waste already included. For an 8-inch wall with every cell grouted that is 36.1 cubic feet per hundred square feet, or about 1.34 cubic yards. An 80-lb bag of grout yields about 0.66 cubic feet.
Per hundred blocks, every cell grouted in an 8-inch wall is about 32.1 cubic feet, scaled from the per-area figure by the blocks in a wall.
What a block wall weighs
The calculator doubles as a concrete block weight calculator for 8-inch walls. CMHA tabulates the wall weight in pounds per square foot by the unit's density class and the grout spacing.
A medium-weight wall ungrouted runs about 31 lb/ft²; with every cell grouted it is about 82 lb/ft², so a 320 square foot wall weighs about 9,920 lb ungrouted. For the full picture by density class, see how much a concrete block weighs. The calculator carries CMHA's 8-inch rows only.
Worked example: a 40 by 8 foot wall
A 40 by 8 ft wall is 320 square feet. At 1.125 blocks per square foot that is 360 blocks, or 378 blocks with the 5% waste allowance. Premixed mortar runs 24 to 32 bags; mixed from masonry cement it is about 13 bags plus 1.58 tons of sand.
Block foundation walls
A block foundation calculator answers the same quantity question: length times height, minus openings, times 1.125 blocks per square foot. What this tool does not do is the structural design, the footing size, the rebar and grout schedule, or the waterproofing. Those come from your plans or an engineer; the calculator gives the block, mortar and grout counts once the wall is specified.
Block wall cost
For a block wall cost, enter your price per block and per mortar bag; the calculator multiplies them by the counts. There is no national block price to default to, so cost lines appear only once you enter a price. Local supply, the weight class and the job size move the number more than any published average would capture.
Concrete block calculator FAQ
How many concrete blocks do I need?
A standard 8x16 unit covers 8/9 of a square foot of wall, so a wall takes 1.125 blocks per square foot. Multiply your wall area by that and add waste. A 320 square foot wall works out to about 378 blocks.
How much block fill do I need per 100 blocks?
For an 8-inch wall with every cell grouted, about 32.1 cubic feet per hundred blocks, from the CMHA grout table (it already includes waste). Convert that to 1.34 cubic yards per hundred square feet or 80-lb bags in the calculator.
How many blocks are in a 1,000-square-foot wall?
About 1,125 blocks before waste, or about 1,182 blocks with the CMHA 5% allowance. CMHA's estimating figure is 119 blocks per hundred square feet.
How much does 1,000 blocks cost?
Block prices vary by region, weight class and supplier, so this calculator has no default price. Enter your price per block and per mortar bag for a wall cost; without a price it shows quantities only.
Sources
- Concrete Masonry & Hardscapes Association (CMHA, formerly NCMA). TEK 04-02A, Estimating Concrete Masonry Materials. TEK 04-02A (page modified Mar 2024)
- Headquarters, Department of the Army. FM 5-428, Concrete and Masonry (18 June 1998), Chapter 8 Concrete Masonry. Jun 1998
- Concrete Masonry & Hardscapes Association (CMHA, formerly NCMA). Tech Note CMU-TEC-001-23, Concrete Masonry Unit Shapes, Sizes, Properties, and Specifications. 2023 edition (-23)
- Sakrete of North America. Technical Data Sheet: Mortar Mix Type S (Rev. 05/18). Rev. May 2018
- The QUIKRETE Companies. QUIKRETE Mortar Mix No. 1102 Data Sheet (Revised November 2020). Revised Nov 2020
- The QUIKRETE Companies. QUIKRETE Masonry Cement (Type N) No. 1125-70 Data Sheet. undated sheet, retrieved Nov 2026
- Concrete Masonry & Hardscapes Association (CMHA, formerly NCMA). Tech Note CMU-TEC-002-23, Weights and Section Properties of Concrete Masonry Assemblies. 2023 edition (-23)
- How Much Does a Concrete Block Weigh?Block weight by ASTM density class, the 8x8x16 ranges, and what a grouted wall weighs per sq ft.
- Brick Calculator: Bricks, Mortar & CostBricks from the makers’ coursing formula, mortar bags, and the per-square-foot count by size.
- Concrete Weight CalculatorTons, pounds and kilograms for a slab, footing or load of concrete, with the reinforced case.