Why does a block sold as 8x8x16 measure 7 5/8 by 7 5/8 by 15 5/8 inches? The label is a nominal size, and the specified size is smaller. This guide covers sizes, shapes and classes, not wall counts.
A standard concrete block has a nominal face of 8 in high by 16 in long, in nominal thicknesses from 4 to 16 in. Specified dimensions are typically 3/8 in less, so a nominal 8x8x16 measures 7 5/8 x 7 5/8 x 15 5/8 in. ASTM C90 sets a 2,000 psi minimum strength.
What Do Nominal and Specified Block Sizes Mean?
Nominal dimensions are the module size used to plan bond patterns and openings, while specified dimensions are the size the unit is made to. CMHA (the Concrete Masonry & Hardscapes Association, the former NCMA) says specified dimensions are typically 3/8 in less than nominal.
That gap lets a 4 in or 8 in module hold with 3/8 in mortar joints. The steps below are our own arithmetic from the CMHA figures.
- Start with nominal. The standard unit is 8 x 8 x 16 in.
- Subtract 3/8 in. 8 – 3/8 = 7 5/8 in, and 16 – 3/8 = 15 5/8 in. CMHA’s Figure 2 shows 7 5/8 x 7 5/8 x 15 5/8 in, and Angelus Block gives the same as 7.625 x 7.625 x 15.625.
- Add one joint back. 15 5/8 + 3/8 = 16 in, and 7 5/8 + 3/8 = 8 in.
That is why nominal sizes stack in whole 8 in courses.
How Much Wall Face Does One Block Cover?
A nominal 16 x 8 in face is 128 sq in, or 0.8889 sq ft. One block therefore covers about 0.89 sq ft of wall. This is arithmetic from the nominal size, which includes the joint.
Dividing 1 by 0.8889 gives 1.125 blocks per sq ft. A half-high face, nominal 16 x 4 in, is 64 sq in, or 0.4444 sq ft, which is 2.25 blocks per sq ft.
Face area uses height and length only, so the width does not change it. The Angelus Block page writes sizes as width x height x length, so a 4x8x16 unit is 4 in wide, 8 in high and 16 in long. The block calculator offers a standard 8x8x16 and a half-high 8x4x16, both nominal sizes with a 3/8 in joint. To turn a wall size into a block total, use the block calculator for wall counts. For poured walls, see the concrete wall calculator.
Which Widths Do Concrete Blocks Come In?
CMHA Tech Note CMU-TEC-001-23 lists nominal thicknesses of 4, 6, 8, 10, 12, 14 and 16 in. Angelus Block, one manufacturer, lists specified widths for its precision units at the 8 in by 16 in nominal face.
Angelus lists the same 7.625 in height and 15.625 in length for each of those units. Each specified width in the chart is 3/8 in under its nominal width. The chart does not show a 14 in row for Angelus, because the page read does not list one.
Which Block Shapes and Types Exist?
CMHA’s tech note names stretcher, corner, open-end, bond beam, lintel, sash, kerf, half-high, split and slump units. The Angelus Block catalog adds product names such as half, U-lintel and bullnose.
| Unit | What the source says | Source |
|---|---|---|
| Stretcher, single corner, double corner (plain end) | Named as shapes; the notes read give no description | CMHA |
| Open-end (“A”) and double open-end | Named as shapes; Angelus also lists open-end standard blocks | CMHA, Angelus |
| Bond beam and knock-out bond beam | Named as shapes; Angelus lists bond beam, open-end and double open-end versions | CMHA, Angelus |
| Lintel | Like a bond beam unit, but the bottom is solid to keep grout in the lintel; Angelus lists U-lintel types | CMHA, Angelus |
| Sash | Has a vertical groove molded into one end | CMHA |
| Kerf (all-purpose) | Splits on the jobsite into two half-length units | CMHA |
| Half-high | Nominal height of 4 in; Figure 8 shows a specified height of 3 5/8 in | CMHA |
| Split and slump | Split has a natural stone-like face; slump has a rounded face like handmade adobe | CMHA |
| Half, bullnose | Listed as products, such as an 8x8x8 half; single and double bullnose are special order | Angelus |
CMHA says other nominal faces also fit the 8 in module, with nominal heights of 4 in and nominal lengths of 24 to 32 in. In the Angelus catalog, an 8x8x24 standard block and an 8x8x12 half are marked special order.
Angelus flags many catalog items as special order or limited inventory. Availability depends on the maker and the item, and the sources do not say any type is stocked everywhere.
Are Blocks Hollow or Solid, and What Are the Density Classes?
CMHA says ASTM C90 units may be made hollow or solid in cross-section. Density is a separate measure, and CMHA sorts units into three oven-dry classes.
Lightweight is under 105 lb/ft3. Medium weight is 105 up to but not including 125. Normal weight is 125 lb/ft3 or more.
How Strong Is a Block, and How Exact Is Its Size?
CMHA lists a minimum net-area compressive strength of 2,000 psi (13.8 MPa) for ASTM C90 units. A March 27, 2026 ICC Building Safety Journal article says the 2011 revision of C90 raised the minimum from 1,900 psi to 2,000 psi.
The ICC article says “net compressive strength,” while CMHA says net-area. The C90 standard itself is paywalled and was not read; these figures come from the two articles.
CMHA also gives a size tolerance. Overall width, height and length can vary from specified by no more than plus or minus 1/8 in, with split-face and slump faces as exceptions. For a 7 5/8 in height, that is 7 1/2 to 7 3/4 in, by our arithmetic. Angelus gives the same plus or minus 1/8 in for its standard precision units.
Angelus also lists slumpstone 6-high units at a height of 5.5 in. CMHA lists slump faces as an exception to the tolerance above.
How Heavy Is a Block, and What Should You Check Before Ordering?
No single official weight appears in the sources read. A Masonry Society journal abstract reports survey averages. They are about 37 lb for normal weight and 26 lb for lightweight 8 in standard blocks. The abstract states no survey date.
CMHA adds that a lightweight 12 in unit can weigh less than a normal-weight 8 in unit. Weights vary by maker, so the supplier is the source for a given unit.
- Say which size you mean. Nominal and specified dimensions differ by 3/8 in.
- Name the unit type. Use the terms in the table above, such as bond beam or half-high.
- Ask about special order. One catalog flags many items that way.
- Ask for the density class and weight. Both come from the maker.
Enter your wall size in the Concrete Block Calculator. Related tools: the foundations and footings calculators and the brick and mortar calculator.
Keep reading: retaining wall height limits, how deep footings should be and rebar sizes and what the numbers mean.
More: all construction guides.
FAQs About Concrete Block Sizes
What is a standard concrete block size?
A standard block has a nominal face of 8 in high by 16 in long. A nominal 8x8x16 block has specified dimensions of 7 5/8 x 7 5/8 x 15 5/8 in, per CMHA.
Why is an 8 in block really 7 5/8 in?
Specified dimensions are typically 3/8 in less than nominal. That leaves room for a 3/8 in mortar joint, so a 7 5/8 in block plus the joint fills 8 in.
What are the actual widths of 4, 6, 8, 10, 12 and 16 in blocks?
Angelus Block lists specified widths of 3.625, 5.625, 7.625, 9.625, 11.625 and 15.625 in for those nominal widths. Confirm other makers’ sizes with your supplier.
What is a half-high block?
A half-high block has a nominal height of 4 in instead of 8 in. CMHA’s Figure 8 shows a specified height of 3 5/8 in.
What are bond beam and lintel blocks?
A lintel unit resembles a bond beam unit, but its bottom is solid so grout stays in the lintel, per CMHA. The same tech note also names bond beam units.
What is the minimum block strength under ASTM C90?
CMHA lists a minimum net-area compressive strength of 2,000 psi (13.8 MPa) for ASTM C90 units.
How heavy is a concrete block?
No single official weight appears in the sources read. A Masonry Society abstract gives survey averages of about 37 lb for normal weight and 26 lb for lightweight 8 in blocks.
Sources and Further Reading
References Used in This Article
- Concrete Masonry & Hardscapes Association, Tech Note CMU-TEC-001-23, Concrete Masonry Unit Shapes, Sizes, Properties, and Specifications, accessed 2026-10-19.
- Angelus Block, Dimensions and Sizes, accessed 2026-10-19.
- Angelus Block, Precision CMU catalog, accessed 2026-10-19.
- The Masonry Society Journal, State-of-the-Art of Concrete Masonry Units (abstract), accessed 2026-10-19.
- ICC Building Safety Journal, What’s Changed in ASTM C90 and TMS 602 Since 2000, accessed 2026-10-19.
The figures here come from CMHA, one manufacturer and a journal abstract. Block sizes and availability vary by maker and region, so confirm specified dimensions with your supplier. Reviewed for accuracy by Prof. Dr. Khalil Mudassar, PhD. Last updated 2026-10-19.
Shakeel Muzaffar is the Founder and Editor-in-Chief, with over 15 years of experience in digital publishing and online tool development. He oversees editorial quality and formula verification to ensure accurate, practical, and easy-to-use calculators.