Concrete (Cinder) Block Calculator
Enter a wall's length and height and get concrete blocks and mortar bags, rounded up once, with the working shown for an example wall. Take off door and window area, pick the block width, and choose whose mortar yield figure to use.
Estimates for planning, not professional advice. Read the full notice.
Example: a block wall
142 blocks
- Wall area 120 ft²
- Blocks in the wall, exact 135 blocks
- Mortar bags at the maker's figure 11 × 80 lb bags
- Grout if every cell is filled 1.6 yd³
Estimate for planning, from what you entered and the product data shown. Check product labels and your supplier before you buy.
Your project
Enter a size to see your total.
Each product is rounded up once for the whole project, so the total can be less than the items bought alone added together. A line counted from a cut layout (sheets, boards or tiles laid out piece by piece) is counted for each item and added.
Shopping list
| Item | Size | Buy |
|---|---|---|
| Concrete blocks | blocks | 142 |
| Mortar mix | 80 lb bag | 11 |
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Worked example: a block wall
Show the working
- Wall area: length times height 20 ft × 6 ft = 120 ft²
- Blocks: area divided by the face of one block 120 ft² ÷ 0.888889 ft² = 135 blocks
- Add the waste allowance, once 135 blocks × 1.05 = 141.75 blocks
- Round up once, to whole blocks 141.75 blocks = 142 blocks
- Mortar bags: net blocks divided by blocks per bag, rounded up once 135 blocks ÷ 13 blocks per bag = 11 × 80 lb bags
Assumptions
The figures behind the example. Sourced figures link to their source below; a default is a starting value to check against your label or supplier.
| Assumption | Value | Details and changes |
|---|---|---|
| Block waste allowance | 5%[1] | |
| Default CMHA's per-100 ft2 figure includes this much waste. | ||
| Blocks per hundred square feet of wall, CMHA (waste included) | 119 units per 100 ft²[1] | |
| CMHA: a conventional 8 in by 16 in nominal block shows 8/9 ft2 of wall; with 5 percent waste that is 119 units per 100 ft2 of wall. | ||
| Blocks one bag lays, QUIKRETE (up to) | 13 blocks[2] | |
| QUIKRETE says an 80 lb bag lays up to this many standard bricks or 8 in by 8 in by 16 in blocks. | ||
| Blocks one bag lays, SAKRETE (no waste allowance) | 12 blocks[3] | |
| SAKRETE says an 80 lb bag of Type S mortar lays this many 8 in blocks or standard bricks, with no allowance for waste or spillage. | ||
| Blocks one bag lays, CMHA preblended (waste included) | 16 blocks[1] | |
| CMHA: one 80 lb bag of preblended mortar lays about this many conventional blocks or brick-sized units; the values include nominal waste and assume face shell bedding for blocks. | ||
Feet and inches, like 12' 6"
Mortar bags by each maker's yield
Bags of mortar mix for the example wall at each maker's blocks-per-bag figure, counted on the net blocks
| Figure | Blocks per 80 lb bag | Bags for the example wall |
|---|---|---|
| QUIKRETE Mortar Mix, up to | 13 blocks (per QUIKRETE's data sheet, checked Nov 12, 2026) | 11 × 80 lb bags |
| SAKRETE Type S, no waste allowance | 12 blocks (per SAKRETE's data sheet, checked Nov 12, 2026) | 12 × 80 lb bags |
| CMHA preblended, waste included | 16 blocks | 9 × 80 lb bags |
Product names are trademarks of their owners. HoneyDoMath is not affiliated with, sponsored by or endorsed by these makers. Figures come from each maker's published sheets and are shown for information only.
The three figures count different things: one is an up-to figure, one leaves out waste and spillage, and one already includes waste. The bags are counted on the net blocks, never on the blocks bought.
Grout in the example wall by how often cells are filled
CMHA grout volume per hundred square feet of an eight inch wall, and the volume for the example wall
| Cells filled | Cubic feet per 100 square feet of wall | Cubic yards for the example wall |
|---|---|---|
| Every cell | 36.1 ft³ | 1.6 yd³ |
| Every 16 in | 18.1 ft³ | 0.8 yd³ |
| Every 24 in | 12.1 ft³ | 0.54 yd³ |
| Every 32 in | 9.1 ft³ | 0.4 yd³ |
| Every 48 in | 6.1 ft³ | 0.27 yd³ |
Source: [1]
CMHA's volumes assume two-core hollow units and three percent waste. The calculator counts blocks and mortar; the grout here is for the example wall only.
Questions
How many blocks do I need for a shed wall?
Type the wall's length and height, take off any door or window area, and the calculator counts blocks on the nominal block face with your waste allowance, rounded up once. A wall that is not a whole number of blocks long or high is counted in whole blocks in every course, so the count is never lower than the blocks you can lay. The worked example shows the steps for one wall, whose size is a whole number of blocks.
How many 8x8x16 blocks are in a hundred square feet?
CMHA gives a figure per hundred square feet of wall that already includes five percent waste, listed in the assumptions. The calculator counts the net blocks from the face and adds your own waste allowance, so do not add waste to CMHA's figure a second time.
What is the difference between nominal and actual block size?
Nominal sizes include the mortar joint, so the wall is counted on the nominal face. Actual sizes are about three eighths of an inch smaller, as CMHA's TEK 05-12 says, and the block sizes page lists both.
Does the calculator count grout?
Not in the live result. The grout table on this page gives CMHA's volume by how often cells are filled, worked out for the example wall.
Sources (3)
-
TEK 04-02A, Estimating Concrete Masonry Materials (opens in new tab), Concrete Masonry & Hardscapes Association (formerly NCMA), TEK 04-02A (web edition).
Standards or industry body.
“nominal heights of 8 in. … and nominal lengths of 16 in. … the exposed surface area of a single unit in the wall is 8/9 ft2 … Including a 5 percent allowance for waste and breakage, this translates to 119 units per 100 ft2 … of wall area.”
“Preblended mortar: 1-80 lb (36.3 kg) bag 16 50 ... Values include nominal amounts for waste. Assumes face shell mortar bedding for conventional concrete masonry units and full bedding for brick-sized concrete masonry units.”
“Volume of grout, ft3 per 100 ft2 of wall (m3 per 100 m2). Wall width: 6 in. (152 mm), 8 in. (203 mm), 10 in. (254 mm), 12 in. (305 mm). Grout spacing 8 (203): 25.6(7.8) 36.1(11.0) 47.0(14.3) 58.9(18.0). ... Assumes two-core hollow concrete masonry units and 3% waste.”
“Volume of grout, ft3 per 100 ft2 of wall … Wall width: … 8 in. (203 mm), … Grout spacing … 16 (406): … 18.1(5.5) … 24 (610): … 12.1(3.7) … 32 (813): … 9.1(2.8) … 48 (1,219): … 6.1(1.9) … Assumes two-core hollow concrete masonry units and 3% waste.”
Checked November 12, 2026. Figures and codes change; verify with the source. Back to where this is used (Source 1) -
QUIKRETE Mortar Mix No. 1102 data sheet (opens in new tab), The Quikrete Companies, Revised November 2020.
Manufacturer data.
“Each 80 lb (36.2 kg) bag of QUIKRETE Mortar Mix will lay up to 37 standard bricks or 13 standard (8 in by 8 in by 16 in [200 mm by 200 mm by 405 mm]) blocks.”
Per QUIKRETE's data sheet, checked Nov 12, 2026. Figures and codes change; verify with the source. Back to where this is used (Source 2) -
SAKRETE Mortar Mix Type S technical data sheet (opens in new tab), SAKRETE of North America, 2018 (sakrete.com copy).
Manufacturer data.
“80 lb (36.3 kg) Will lay 12 = 8" (200 mm) concrete block, 35 standard bricks or 10 ft2 (1.0 m2) of cultured stone ... Note: Yield and water are approximate. The yield above does not allow for waste and spillage.”
Per SAKRETE's data sheet, checked Nov 12, 2026. Figures and codes change; verify with the source. Back to where this is used (Source 3)
These are summaries of what the sources say, not professional advice. Codes and product data change. Check with your building department and the product label about your own project.
Sources
- [1] Concrete Masonry & Hardscapes Association (formerly NCMA), TEK 04-02A, Estimating Concrete Masonry Materials. Checked November 12, 2026. https://www.cmha.org/resource/tek-04-02a/
- [2] QUIKRETE, QUIKRETE Mortar Mix No. 1102 data sheet. Checked November 12, 2026. https://www.quikrete.com/PDFs/DATA_SHEET-Mortar%20Mix%201102.pdf
- [3] SAKRETE, SAKRETE Mortar Mix Type S technical data sheet. Checked November 12, 2026. https://www.sakrete.com/wp-content/uploads/2021/07/Mortar-Mix-Type-S.pdf