How many concrete blocks do I need for a wall?
A standard 8 x 8 x 16 inch concrete block covers 0.89 square feet of wall once its 3/8 inch mortar joint is included, so you need 1.125 blocks per square foot: 135 blocks for a 20 ft long, 6 ft high wall, or 142 with 5% for breakage and cuts. The tables give common wall sizes, the mortar to go with them, and the metric 440 x 215 mm block.
Open the concrete block calculator
Blocks per square foot and for common walls
The 8 x 8 x 16 inch block is actually 7 5/8 x 7 5/8 x 15 5/8 inches; the 3/8 inch mortar joint brings it back to a nominal 16 x 8 inches on the face of the wall. That is 0.889 square feet per block and 1.125 blocks per square foot. The table has 5% waste and no openings; take doors and windows off the area first.
| Wall | Area (sq ft) | Blocks per course | Courses | Blocks | With waste | Mortar (cu ft) |
|---|---|---|---|---|---|---|
| 10 x 4 ft | 40 | 8 | 6 | 45 | 48 | 1.8 |
| 12 x 6 ft | 72 | 9 | 9 | 81 | 86 | 3.2 |
| 20 x 4 ft | 80 | 15 | 6 | 90 | 95 | 3.5 |
| 20 x 6 ft | 120 | 15 | 9 | 135 | 142 | 5.3 |
| 30 x 8 ft | 240 | 23 | 12 | 270 | 284 | 10.6 |
| 40 x 8 ft | 320 | 30 | 12 | 360 | 378 | 14.1 |
How the numbers are worked out
Wall area divided by the face area of one block plus its joint gives the count; multiply by 1.05 for waste and round up. As a check, count blocks per course (length in inches divided by 16) and courses (height in inches divided by 8) and multiply: the two methods agree, and the course count also tells you whether the wall height lands on a full block. The concrete block calculator handles openings, other block sizes, the mortar bags, and the grout and rebar for the cells; the brick calculator takes any joint width.
Mortar
The tables give mortar as the volume of the wall that is not block: bed joints and head joints, 5.3 cubic feet for the 20 x 6 ft wall. Bagged mortar mix is easier to buy by the label, which says how many blocks an 80 lb bag lays (up to 13 on Quikrete's sheet, 12 on others); divide your block count by that figure and round up and add 10%, which the calculator does for the bag you choose: mortar that dries in the tub is the usual waste.
Metric: 440 x 215 mm blocks per square metre
The common European block is 440 x 215 x 100 mm with a 10 mm joint, which gives a nominal 450 x 225 mm face, or 9.88 blocks per square metre. Blocks and hollow blocks of other sizes are presets in the calculator.
| Wall area | Blocks | With waste | Mortar (m³) |
|---|---|---|---|
| 10 m² | 99 | 104 | 0.066 |
| 20 m² | 198 | 208 | 0.131 |
| 30 m² | 297 | 312 | 0.197 |
| 50 m² | 494 | 519 | 0.328 |
Before you order
- A block wall stands on a footing. Its concrete is worked out separately in the concrete calculator; a typical footing is twice the wall thickness wide and as deep as the wall is thick, below frost depth.
- Corners and the ends of walls use full and half blocks alternately; buy half blocks rather than cutting them.
- Retaining walls, walls over about 4 ft and anything carrying a roof usually need reinforcement, grout-filled cores and a design to local code; the block count is the easy part.
- Building in brick instead? See bricks per square metre and per square foot.
Frequently asked questions
- How many concrete blocks do I need per square foot?
- 1.125 blocks per square foot of wall for the 8 x 8 x 16 inch block with a 3/8 inch joint, which is 112.5 blocks per 100 square feet. The nominal size including the joint is exactly 16 x 8 inches, so 9 blocks make 8 square feet.
- How many blocks are in a course?
- Divide the wall length in inches by 16. A 20 ft wall is 240 inches, so 15 blocks per course, and at 8 inches per course a 6 ft wall is 9 courses: 15 x 9 = 135, the same figure the area method gives.
- How many bags of mortar per block?
- Bag labels are the honest source: an 80 lb bag of mortar mix lays up to 13 standard blocks (Quikrete's data sheet; other brands say 12), so a 20 x 6 ft wall of 135 blocks needs 12 bags with 10% extra for the board and the tub. As a volume the joints of that wall are 5.3 cubic feet, which is what the tables show; the concrete block calculator counts the bags for the bag you pick.
- How many blocks do I need for a wall with a door and a window?
- Take the openings off the area first. A 20 x 6 ft wall with a 3 x 7 ft door and a 3 x 4 ft window has 87 square feet of block, so 98 blocks instead of 135, or 103 with waste. Lintels over the openings are extra.
- How much waste should I add for concrete blocks?
- 5% is enough for a plain wall: blocks are tough and half blocks are sold ready-made. Go to 10% if the wall has many openings, corners or a stepped top, where you will be cutting blocks with a saw and breaking a few.
- How many blocks per square metre?
- About 9.9 of the 440 x 215 mm block with a 10 mm joint, so a 10 m² wall takes 99 blocks, 104 with 5% waste. The 8 x 8 x 16 inch block works out at 12.1 per square metre.
More guides
- How much concrete to fill cinder blocks? (per block, per 100, per wall)
Grout per 8 in block (0.22 cu ft, three blocks per 80 lb bag), per 100 blocks and for 10 to 40 ft walls with every cell filled or bars every 16 to 48 in, plus metric.
- How much does a cinder block wall cost? (materials per wall and per square foot)
Blocks, mortar and grout priced for walls from 10x4 to 40x8 ft at 2026 shelf prices, materials per square foot, what grouting adds, and HomeGuide's installed range.
- Building a block wall: courses, rebar, grout and mortar for a 20 ft wall
The material list for a CMU wall in order: footing, courses, half blocks, bars every 32 or 48 in, grouted cells, bond beam and mortar, with counts for 4 to 8 ft walls.
- How much does a cinder block garage cost? (blocks, mortar, grout and slab for 1, 2 and 3 car)
Blocks, mortar and grout for 1 to 3 car block garages, 12x20 to 36x24 ft, 8 ft walls, doors and windows taken off, plus the 4 in slab, at 2026 prices.
Last updated 2026-09-15. Figures are planning estimates from typical product data: check the yield, size or coverage printed on what you buy and round up.