Concrete Block Calculator: Blocks, Mortar and Grout
Count the concrete blocks (CMU or cinder blocks), mortar bags and core grout a wall needs from its length, height and openings, with waste and cost. List the walls, take off the doors and windows, pick the block size and width, and get the block count, bags of mortar mix, cubic yards of grout for solid or partly grouted cores, and the cost of materials.
Your numbers
Walls
Up to 8 walls, added together.
Doors and windows (optional)
A 36 × 80 in door is 20 sq ft.
A 3 × 5 ft window is 15 sq ft.
Block
Waste
CMHA's estimating guide adds about 5 % for waste and breakage.
Mortar lost on the board and in the joints; the brick calculator uses the same 15 %.
Mortar bags
Quikrete: an 80 lb bag of Mortar Mix lays up to 13 blocks. CMHA puts an 80 lb bag of preblended mortar at about 16. Edit to your mix.
Core grout (optional)
CMHA TEK 04-02A Table 3, two-core units, 3 % waste included. Every core is a solid-grouted wall; 48 in is every sixth core.
Prices (optional)
Blocks to buy
–
- Wall area
- –
- Blocks per square foot
- 1.125
- Blocks before waste
- –
- Block
- 8 × 8 × 16 in nominal
- Bags of mortar mix
- –
- Material cost
- –
An estimate for quoting and buying. Footings, rebar, bond beams, lintels and grout spacing follow the engineer's drawings and your local code.
Corners, pilasters, bond beam and half units are counted separately on a real takeoff; add them to the count or to the waste.
The calculation runs in your browser and ParrotNotes does not store your numbers. They sit in the page address so you can bookmark or share the result.
How to use the concrete block calculator
Enter the length and height of each wall in feet and add as many walls as the job has. Count the doors and windows and set their size; the calculator takes them off the area. Pick the block face and width, then the mortar bag and, if the wall is grouted, how often the cores are filled.
Worked example: a 40 × 6 ft wall is 240 sq ft. Standard 8 × 16 in blocks fill 1.125 per sq ft, so 270 blocks, plus 5% is 284. At 13 blocks per 80 lb bag with 15% extra, the mortar is 23.9, so 24 bags. Solid grouted in 8 in block, the cores take 86.6 cubic feet, 3.21 cubic yards.
Mortar bags for block
Bagged mortar mix is the simplest order for a small wall. Quikrete gives up to 13 blocks per 80 lb bag of its Mortar Mix; CMHA's Table 2 gives about 16 conventional blocks per 80 lb bag of preblended mortar. The difference is how much mortar each mason uses, so change the blocks per bag if your crew knows its own figure.
Larger jobs often mix masonry cement and sand on site. CMHA puts one 70 lb bag of masonry cement at about 30 hollow units, with one ton of sand for every eight bags. Those figures assume mortar on the face shells only, which is how hollow block is normally laid.
Grout and rebar in the cores
Reinforced block walls get vertical bars in some cores and grout around them. CMHA's Table 3 gives the grout in cubic feet per 100 sq ft of wall for 6, 8, 10 and 12 in walls, from every core to one core every 120 in, for two-core units with 3% waste. The calculator uses that table; it does not table 4 in units, which CMHA does not recommend grouting.
The spacing of the bars and the grouted cores comes from the engineer's drawings or the local code. For the steel itself, the Rebar Calculator counts bars, laps and weight.
Block sizes and widths
Block sizes are nominal: the actual unit is ⅜ in smaller each way, which leaves room for the joint. That is why the calculator works from the nominal face and needs no joint setting. A 6 in or 12 in block covers the same wall as an 8 in block; the width changes the weight, the grout and the price, not the count.
For an odd unit, choose Custom face and type the nominal height and length. A real takeoff also counts corner, pilaster, bond beam and half units separately; add them to the count or allow for them in the waste.
For masons and block-wall contractors
The numbers in a block quote come from the walk-through: each wall, the openings, the block the customer picked, where the footing steps, how the trucks reach the site and what the engineer wants grouted. A missed opening or a wall not written down means a second trip or a pallet short on the day.
Sources, each read on 2026-10-24. All results are estimates; your supplier and engineer decide:
More for building-materials and contractor sales: Building materials sales, Construction daily report, Quote follow-up email.
The wall is measured on the walk-through
Wall lengths, the openings, the block the customer wants and where the engineer calls for grout all get said on site. Record the walk-through in ParrotNotes and get a transcript, a summary and the action items, so the takeoff matches what was measured and agreed.
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