Concrete & Masonry
Concrete Block Calculator
Enter wall length and height, subtract any openings, and get the number of standard 8 x 8 x 16 in blocks, the courses and the premixed mortar to buy.
Worked example
- Wall area = 40 x 4 - 0 = 160 sq ft.
- An 8 x 16 in block face covers 0.889 sq ft, so 1.125 blocks per sq ft: 160 x 1.125 = 180, plus 5% = 189 blocks.
- Mortar: about 6.25 bags of 80 lb premixed mortar per 100 blocks = 12 bags.
Common sizes at a glance
| Size | Blocks (8 x 8 x 16 in) | 80 lb mortar bags |
|---|---|---|
| 20 ft x 3 ft wall | 71 | 5 |
| 40 ft x 4 ft wall | 189 | 12 |
| 24 x 24 ft foundation, 4 ft | 454 | 29 |
| 30 x 40 ft foundation, 8 ft | 1,323 | 83 |
One block covers less than one square foot
A standard block is nominally 8 x 16 in on its face, which already includes a 3/8 in mortar joint. That face covers about 0.889 sq ft, so a wall needs 1.125 blocks for every square foot.
In the worked example, a 40 ft wall that is 4 ft high has 160 sq ft of face. That works out to 180 blocks, or 189 once a 5% allowance for breakage and cuts is added.
Courses and blocks per row
Because each course is 8 in tall, a 4 ft wall has 6 courses, and a 40 ft run has 30 blocks per course. Seeing the rows helps you stage pallets along the wall instead of in one pile.
If your wall height is not a multiple of 8 in, the top course will need cut blocks or a cap. Planning the height in 8 in steps saves cutting.
Openings, corners and special blocks
Subtract doors and windows as square feet. Remember that openings and corners often call for special units, like half blocks, corner blocks or lintel blocks, which are bought separately from the standard count.
Walk the plan and list those pieces by hand. Pallet-quantity standard blocks are easy to buy; a missing pair of corner blocks can stall the job for a day.
Mortar and grout
We estimate about 6.25 bags of 80 lb premixed mortar per 100 blocks, so the 189-block wall needs 12 bags. The mortar calculator works from wall area if you want to check that number.
If cores are filled with grout, that is a separate material from mortar. Which cores get grout and steel is set by the plans, the local building code and a licensed professional, not by a material calculator.
Below the wall
A block wall sits on a concrete footing. Use the concrete footing calculator to figure the concrete for the size your plans show.
Questions
How many blocks are in 100 square feet of wall?
About 113 blocks of 8 x 8 x 16 in, before any waste allowance.
How many blocks for a 24 x 24 foundation 4 ft tall?
About 454 blocks and 29 bags of 80 lb mortar, as the common sizes table shows.
Does this work for 6 in or 12 in blocks?
The face size of 8 x 16 in is the same on most widths, so the count holds; the grout and weight change.
How this works: formulas and typical values are listed on our method page; every data source and its license is on sources.
Last reviewed November 2026.