Modular Brick: Dimensions, Mortar Joints and Coverage
US modular brick dimensions: specified versus actual size, the 4 × 2⅔ × 8-inch nominal module, mortar joints and bricks per square foot.
A common US modular brick has specified dimensions of 3⅝ in. wide × 2¼ in. high × 7⅝ in. long—approximately 92 × 57 × 194 mm, excluding mortar. Its nominal dimensions are 4 × 2⅔ × 8 in., including the intended joints and vertical coursing. These are the dimensions listed in the Brick Industry Association’s Technical Note 10.
The important distinction: adding a ⅜-in. joint to every dimension does not produce that nominal height. The horizontal module and vertical coursing need separate checks.
Specified, actual and nominal dimensions
| Dimension term | Common modular-brick size, width × height × length | What it describes |
|---|---|---|
| Specified | 3⅝ × 2¼ × 7⅝ in. | Intended manufactured dimensions, without mortar; used for specifications and purchase orders |
| Actual | Measured on the supplied units | Manufactured dimensions, which may differ from the specified size within applicable tolerances |
| Nominal | 4 × 2⅔ × 8 in. | Coordinating dimensions incorporating intended joints and coursing |
BIA distinguishes all three terms and notes that names and specified sizes can vary by manufacturer. Check the selected product rather than treating “modular” as a complete dimensional specification. Its metric figures are conversions of US inch-based sizes, not interchangeable dimensions for a 100-mm modular system. Source: BIA Technical Note 10.
How the mortar joints complete the module
For the common size above, a ⅜-in. head joint gives an 8-in. horizontal repeat:
7⅝ in. brick length + ⅜ in. joint = 8 in.
The width also fits the corner relationship:
2 × 3⅝ in. brick widths + ⅜ in. joint = 7⅝ in. brick length.
These relationships help brickwork turn corners and maintain its bond with limited cutting. See running bond for how successive courses are offset.
Vertically, BIA’s nominal module is three courses in 8 in., counting three bricks and three bed joints. With 2¼-in.-high units, the calculated average bed joint needed is 5⁄12 in., approximately 0.417 in. This is a calculation for that coursing, not a universal joint specification. BIA notes that actual bed-joint thickness depends on the required coursing and actual brick height. Source: BIA Technical Note 10.
By comparison, using exactly ⅜-in. bed joints produces a 2⅝-in. course repeat and 7⅞ in. over three repeats, not 8 in. Establish the intended coursing before setting out openings or adjoining masonry.
Modular versus standard brick
“Standard” is also a supplier size name, not necessarily a synonym for modular. Belden’s dimension guide lists:
- Modular: 3⅝ × 2¼ × 7⅝ in.
- Standard: 3⅝ × 2¼ × 8 in.
The standard unit is ⅜ in. longer before mortar. Substituting it changes the horizontal repeat and brick count even though its height and width match.
How many modular bricks per square foot?
For a single wythe laid with the stretcher face exposed, the answer depends on the joint and coursing assumptions:
- 6.86 bricks/ft²: Belden’s published count for modular face brick with ⅜-in. joints. The calculation is 144 ÷ [(7⅝ + ⅜) × (2¼ + ⅜)]. Source: Belden.
- 6.75 bricks/ft²: BIA’s nominal-module estimate, equivalent to 675 bricks per 100 ft², using an 8 × 2⅔-in. face module. This excludes waste. Source: BIA, Table 4.
The difference is not a waste allowance. These are wall-face counts, not paving counts or totals for a multi-wythe wall. Multiply net wall area by the count appropriate to the selected brick and layout, then adjust for bond, cuts and breakage. BIA’s table assumes running or stack bond; patterns incorporating headers need corrections. BIA gives at least 5% as a general brick-waste allowance, added after those corrections, with more where job conditions warrant it. Source: BIA, Correction Factors.
For ordering, record the manufacturer, product, specified width × height × length, head-joint width and vertical coursing. Obtain a separate count for special shapes rather than assuming every corner, sill or decorative course uses ordinary stretchers.