Concrete block calculator
A wall 40 ft long and 4 ft high takes 189 standard blocks with 5% extra and 15 bags of 80 lb mortar mix. Grouting every core adds 60 bags of core-fill grout.
Blocks per square foot
A standard block is sold as 8 × 8 × 16 in, but those are nominal sizes: the block itself is 7⅝ × 7⅝ × 15⅝ in, and a ⅜ in mortar joint brings each one up to 8 × 16 in on the face of the wall. One square foot is 144 square inches, so a wall needs 144 ÷ 128 = 1.125 blocks per square foot. The same face size applies to 4, 6, 10 and 12 in wide blocks, so their count is the same. Half-high blocks (4 × 16 in face) need twice as many.
40 ft × 4 ft = 160 sq ft
144 sq in ÷ (8 × 16 in) = 1.125 blocks per sq ft × 160 sq ft = 180 blocks
Each course is 8 in high and each block covers 16 in of length, so you can also count courses: a 4 ft wall is 6 courses, and every 10 ft of wall takes 7½ blocks per course.
Mortar and grout
QUIKRETE says one 80 lb bag of its Mortar Mix or Mason Mix lays up to 13 standard blocks. That is the most a bag will lay, so treat the bag count as a minimum and keep a spare bag or two on site. If the wall has reinforcing steel, the cores with rebar are filled with grout. QUIKRETE's Core-Fill Grout yields about 0.68 cu ft per 80 lb bag and fills the cores of about 3 standard 8 in blocks. Your plans or building department will say which cores to fill; choose the spacing in the calculator.
Blocks for common walls
| Wall | Blocks (exact) | With 5% extra | Mortar bags | Grout bags, every core |
|---|---|---|---|---|
| 10 × 4 ft | 45 | 48 | 4 | 15 |
| 20 × 4 ft | 90 | 95 | 8 | 30 |
| 20 × 6 ft | 135 | 142 | 11 | 45 |
| 30 × 4 ft | 135 | 142 | 11 | 45 |
| 40 × 8 ft | 360 | 378 | 30 | 120 |
| 60 × 8 ft | 540 | 567 | 44 | 180 |
| 100 × 8 ft | 900 | 945 | 73 | 300 |
Sources
- QUIKRETE Mortar Mix (No. 1102) and Mason Mix (No. 1136) data sheets, The QUIKRETE Companies, revised November 2020. An 80 lb bag lays up to 37 standard bricks or 13 standard 8 x 8 x 16 in blocks.
- QUIKRETE Core-Fill Grout, Fine (No. 1585-08) data sheet, The QUIKRETE Companies, current sheet. An 80 lb bag yields about 0.68 cu ft and fills the cores of about 3 standard 8 x 8 x 16 in blocks.