Concrete Masonry Guide
Concrete Block Sizes
Learn the standard concrete block sizes and dimensions used in masonry construction. Compare common CMU sizes, actual and nominal dimensions, block widths, wall applications, and how block size affects the number of blocks you need.
Quick Answer
What is the standard concrete block size?
A common standard concrete masonry unit (CMU) has a nominal face size of 8 × 16 inches. The actual dimensions are typically slightly smaller to allow for mortar joints, with the exact dimensions depending on the manufacturer and block type.
Concrete blocks are also available in different widths, including 4, 6, 8, 10, and 12 inches. Specialty blocks can have different lengths, heights, shapes, and configurations for corners, openings, columns, and other masonry details.
If you are using a specific block size for a wall project, enter that size into the Concrete Block Calculator to estimate how many blocks you need.
Standard Concrete Block Sizes
Concrete blocks are manufactured in several standard dimensions to accommodate different wall thicknesses and construction requirements. The most commonly recognized CMU size has a nominal face dimension of 8 inches high by 16 inches long.
The width of the block changes depending on the required wall thickness. This means two blocks can have the same 8 × 16 inch face dimensions while having different widths.
| Nominal size | Typical actual size | Common use |
|---|---|---|
| 4 × 8 × 16 in | Approx. 3⅝ × 7⅝ × 15⅝ in | Thin partitions and non-load-bearing applications |
| 6 × 8 × 16 in | Approx. 5⅝ × 7⅝ × 15⅝ in | Partitions and lighter masonry walls |
| 8 × 8 × 16 in | Approx. 7⅝ × 7⅝ × 15⅝ in | Common walls, foundations, and general masonry |
| 10 × 8 × 16 in | Approx. 9⅝ × 7⅝ × 15⅝ in | Thicker walls and structural applications |
| 12 × 8 × 16 in | Approx. 11⅝ × 7⅝ × 15⅝ in | Thicker structural and foundation walls |
Concrete block dimensions can vary by manufacturer, product type, and region. Always check the manufacturer's specifications before ordering materials or using dimensions for structural work.
Concrete Block Dimensions Explained
Concrete block dimensions are normally described using three measurements: width, height, and length. For example, an 8 × 8 × 16 inch block is approximately 8 inches wide, 8 inches high, and 16 inches long by its nominal dimensions.
Width
The width determines the thickness of the masonry unit and is important when planning the overall wall thickness.
Height
The height determines how many courses of blocks are required to reach the desired wall height.
Length
The length determines how many blocks are needed along the length of the wall.
Nominal vs. Actual Concrete Block Size
One of the most important things to understand when working with CMU dimensions is the difference between nominal size and actual size.
A block described as an 8 × 8 × 16 inch block does not necessarily measure exactly 8 × 8 × 16 inches. The nominal dimensions are used as a convenient construction size that accounts for the mortar joint between blocks.
A typical nominal 8 × 8 × 16 inch block may have actual dimensions around 7⅝ × 7⅝ × 15⅝ inches. When a mortar joint is included, the installed module is approximately 8 × 8 × 16 inches.
Nominal
8 × 8 × 16 inThe construction size commonly used when planning masonry layouts.
Actual
Approx. 7⅝ × 7⅝ × 15⅝ inThe physical dimensions of a typical block before installation.
Common CMU Concrete Block Sizes
CMU stands for concrete masonry unit. The term is commonly used by architects, engineers, contractors, masons, and building suppliers to describe manufactured concrete masonry blocks.
Common CMU sizes use an 8-inch nominal height and 16-inch nominal length, while the width changes according to the wall thickness.
4-Inch CMU
A relatively narrow block commonly used where a thinner masonry wall or partition is appropriate.
6-Inch CMU
Used for certain partitions and masonry applications where a 6-inch nominal wall thickness is appropriate.
8-Inch CMU
One of the most common general-purpose CMU sizes used in masonry construction.
10-Inch CMU
Provides a thicker wall and can be used in applications requiring additional wall thickness.
12-Inch CMU
Used where a wider masonry unit is needed for thicker walls and certain structural applications.
How Many Concrete Blocks Per Square Foot?
The number of concrete blocks required per square foot depends on the face dimensions of the block and the mortar joint.
A nominal 8 × 8 × 16 inch block has a face area of approximately 0.89 square feet based on its nominal dimensions:
This means a simple estimate based on nominal dimensions is roughly 1.125 blocks per square foot.
In actual construction, mortar joints affect the installed module and therefore the final block count. Openings, cuts, corners, and waste should also be considered when estimating a real project.
Don't rely on a generic blocks-per-square-foot number if you already know the exact block size. Enter your wall dimensions and block dimensions into the Concrete Block Calculator for a project-specific estimate.
Concrete Block Sizes for Different Wall Thicknesses
The width of a concrete block is particularly important when planning wall thickness. The block's face dimensions may remain similar while the width changes.
| Nominal width | Approximate actual width | Typical purpose |
|---|---|---|
| 4 in | 3⅝ in | Thin partitions and selected interior applications |
| 6 in | 5⅝ in | Partitions and lighter wall construction |
| 8 in | 7⅝ in | Common masonry and general construction |
| 10 in | 9⅝ in | Thicker masonry walls |
| 12 in | 11⅝ in | Thicker walls and selected structural applications |
Special Concrete Block Sizes and Shapes
Not every concrete masonry unit is a simple rectangular block. Manufacturers produce specialty units to make corners, openings, reinforcement, transitions, and other masonry details easier to build.
Corner Blocks
Designed to create clean corners while maintaining the intended wall layout and appearance.
Half Blocks
Shorter units can help create staggered joints and reduce cutting during construction.
Lintel Blocks
U-shaped or channel-style units can be used in certain reinforced masonry details above openings.
Bond Beam Blocks
Channel-shaped units can accommodate reinforcement and grout where the wall design calls for them.
Column Units
Specialized shapes can be used to create reinforced masonry columns or pilasters.
Split-Face Blocks
Textured units designed to provide a different architectural appearance compared with standard smooth-face CMUs.
Concrete Block Size vs. Cinder Block Size
The terms concrete block and cinder block are often used interchangeably in everyday conversation. However, traditional cinder blocks and modern concrete masonry units are not necessarily made from the same materials.
Modern CMUs can use Portland cement, aggregates, water, and other materials, while historical cinder blocks commonly incorporated industrial cinders as aggregate.
When searching for masonry products, it is more useful to check the manufacturer's actual product dimensions and specifications than to rely only on the name used by a supplier or homeowner.
How Concrete Block Size Affects Your Project
Choosing a block size affects more than the physical thickness of the wall. It can also change the number of blocks required, mortar consumption, handling, installation time, and overall material requirements.
Wider blocks create a thicker masonry wall and may be required for particular applications.
The face dimensions determine how many blocks are needed to cover a given wall area.
Block layout and joint dimensions influence the amount of mortar required for construction.
Larger or heavier units can affect how materials are handled and installed on the job site.
How to Choose the Right Concrete Block Size
The correct block size depends on the wall design and the requirements of the project. The block should not be selected only because it is the most common size.
Consider the required wall thickness, whether the wall is structural or non-structural, the location of the wall, reinforcement requirements, openings, local building requirements, and the manufacturer's available units.
For structural walls, foundations, retaining walls, and other applications where the masonry is part of the building structure, follow the applicable building code and project specifications.
How to Measure a Concrete Block
If you already have blocks on site and don't know their size, measure the three primary dimensions: width, height, and length.
Measure the width
Measure across the thickness of the block.
Measure the height
Measure from the bottom of the block to the top.
Measure the length
Measure across the longest face of the block.
Remember that an existing block may have actual dimensions that are slightly smaller than its nominal construction size.
Concrete Block Size Example
Suppose you are building a wall using nominal 8 × 8 × 16 inch blocks. The nominal face area of one block is:
Convert that to square feet:
Based on nominal dimensions, approximately 1.125 blocks are needed per square foot before considering the actual installed layout, openings, corners, and waste.
If your wall is 240 square feet, a basic estimate would therefore be:
This is a simplified quantity example. For an actual project, use the exact block dimensions, mortar assumptions, openings, and waste allowance.
Calculate Concrete Blocks Using Your Block Size
Nerdds Calculator
Know Your Block Size? Calculate Your Quantity.
Enter your wall dimensions and the block size you plan to use. The Nerdds Concrete Block Calculator helps estimate the number of blocks required while accounting for openings and waste.
Open Concrete Block Calculator →Frequently Asked Questions
What is the standard size of a concrete block?
A common standard concrete block has a nominal face size of 8 × 16 inches, with the block width varying according to the required wall thickness. The actual dimensions are typically slightly smaller than the nominal dimensions.
What size is a standard concrete block?
A commonly used CMU has nominal dimensions of 8 inches high by 16 inches long. Common widths include 4, 6, 8, 10, and 12 inches.
What are common CMU sizes?
Common CMU sizes include 4 × 8 × 16, 6 × 8 × 16, 8 × 8 × 16, 10 × 8 × 16, and 12 × 8 × 16 inches. Specialty units are also available for corners, openings, reinforcement, and architectural applications.
What is the actual size of an 8 × 8 × 16 concrete block?
A typical 8 × 8 × 16 inch nominal CMU may have actual dimensions of approximately 7⅝ × 7⅝ × 15⅝ inches. Exact dimensions vary by manufacturer and product.
How many concrete blocks are in a square foot?
Based on the nominal 8 × 8 × 16 inch face dimensions, approximately 1.125 blocks are needed per square foot. Actual project quantities depend on mortar joints, openings, layout, and waste.
Are concrete blocks and cinder blocks the same size?
They can have similar dimensions, but the terms do not necessarily describe the same material. Modern concrete masonry units and traditional cinder blocks can differ in their aggregate and manufacturing. Check the actual product dimensions when planning a project.
How does concrete block size affect the number of blocks I need?
Larger face dimensions generally cover more wall area per block, while smaller blocks require more units for the same area. Enter your specific block dimensions into the Concrete Block Calculator for a project-specific estimate.