Concrete Block Calculator
Block, mortar, core fill and rebar for a CMU wall.
Blocks to order
378
- Gross wall area
- 320 sq ft
- Net of openings
- 320 sq ft
- Courses
- 12
- Blocks per course
- 30
- Blocks with 5% waste
- 378
- Mortar
- 12 bags
- Cells filled (25%)
- 1.12 yd³
- Vertical rebar
- 80 ft
- Block
- $982.80
- Mortar
- $108.00
- Grout fill
- $201.60
- Rebar
- $68.00
- Labor
- $3,840.00
- Total
- $5,200.40
- Material per sq ft
- $4.25/sq ft
- Installed per sq ft
- $16.25/sq ft
1.125 standard block per square foot of wall — the number every mason quotes.
Laying out horizontal steel as well? Use the rebar calculator →
How this is calculated
block face = (block length × block height) ÷ 144 courses = ceil(wall height × 12 ÷ block height) per course = ceil(wall length × 12 ÷ block length) blocks = ceil(net area ÷ block face × (1 + waste%)) mortar = ceil(blocks ÷ 100 × 3) grout fill = blocks × cells filled% × 0.32 cu ft ÷ 27 rebar = (length × 12 ÷ spacing) × height
The block face includes the mortar joint, which is why a nominal 8 by 16 inch block is figured at exactly 16 by 8 inches rather than its true 15⅝ by 7⅝. That convention is what makes 1.125 block per square foot come out even.
Blocks by wall size
Standard 8 × 8 × 16 block, 5 percent waste, no openings. Same function as the calculator above.
| Wall | Area | Blocks | Mortar bags | Full grout |
|---|---|---|---|---|
| 10 ft × 4 ft | 40 sq ft | 48 | 2 | 0.6 yd³ |
| 20 ft × 4 ft | 80 sq ft | 95 | 3 | 1.1 yd³ |
| 20 ft × 8 ft | 160 sq ft | 189 | 6 | 2.2 yd³ |
| 40 ft × 8 ft | 320 sq ft | 378 | 12 | 4.5 yd³ |
| 50 ft × 8 ft | 400 sq ft | 473 | 15 | 5.6 yd³ |
| 100 ft × 8 ft | 800 sq ft | 945 | 29 | 11.2 yd³ |
Fill volume by block size
| Block | Cu ft per block | Per 100 block | Blocks per yd³ |
|---|---|---|---|
| 8" × 8" × 16" standard CMU | 0.32 | 1.19 yd³ | 84 |
| 12" × 8" × 16" CMU | 0.52 | 1.93 yd³ | 52 |
| 6" × 8" × 16" CMU | 0.24 | 0.89 yd³ | 113 |
| 4" × 8" × 16" CMU | 0.15 | 0.56 yd³ | 180 |
| 8" × 4" × 16" half-height | 0.16 | 0.59 yd³ | 169 |
Frequently asked questions
How many blocks do I need per square foot?
1.125 standard blocks per square foot of wall. A nominal 8 by 8 by 16 inch block covers 16 by 8 inches of face including its mortar joint, which is 0.889 square feet, and one divided by that is 1.125. Every mason quotes that number, and it is why a 320 square foot wall takes 360 block.
How much mortar does a block wall need?
About three 70 pound bags of mortar mix per 100 blocks, which also means roughly 1,000 blocks per ton of masonry cement plus sand. Cold weather, wide joints and an inexperienced mason all push consumption up, so buying a few bags over is cheap insurance against stopping mid-wall.
How much grout does it take to fill the cells?
About 0.32 cubic feet per standard 8 inch block when every cell is filled, so 100 blocks take roughly 1.2 cubic yards. Twelve inch block nearly doubles that. Most residential walls only fill the cells that carry rebar rather than all of them, which cuts the grout sharply.
Do I have to fill every cell?
No, and most walls do not. Codes typically require grout only in the cells containing vertical reinforcement, at corners and around openings. Fully grouted walls are for retaining, tall walls and high seismic or wind zones. This calculator lets you set the percentage rather than assuming all or nothing.
How much does a block wall cost?
Material alone commonly lands between $3 and $6 per square foot of wall. Installed by a mason, expect $10 to $25 per square foot depending on height, access, reinforcement and finish. Block itself is the cheap part — the labor of laying it is most of the number.
Does this work for a foundation or a retaining wall?
It counts the material correctly, but it does not engineer anything. A block foundation or a block retaining wall needs footing size, rebar schedule and grout spacing from an engineer or from your local code, since the loads and the soil decide those, not the block count.
Material estimates only. This does not size footings, rebar schedules or grout spacing — those come from your local code or an engineer, and they depend on loads and soil, not on block counts.