A standard 8×8×16 concrete block (cinder block or CMU) has nominal dimensions of 8" × 8" × 16" and actual specified dimensions of 7-5/8" × 7-5/8" × 15-5/8" (190 × 190 × 390 mm) to accommodate a standard 3/8" mortar joint. Select any block width or shape below to inspect exact ASTM C90 geometry and check modular wall course alignment.
1. Select Nominal Block Width (Thickness)
2. Select CMU Block Shape / Unit Type
Selected CMU Spec
7-5/8" × 7-5/8" × 15-5/8"
Nominal Module: 8" × 8" × 16" • Joint: 3/8" (0.375")
Enter your target wall length and height to test whether it lays out cleanly on the 8" (200 mm) CMU modular grid without saw cutting blocks.
Concrete masonry units (CMUs)—commonly called concrete blocks, cinder blocks, or cement blocks—are manufactured in five standard nominal widths under ASTM C90. While face height (8") and length (16") stay constant across standard stretchers, wall thickness scales from 4" partition units to 12" foundation units.
| Nominal Size (W × H × L) | Actual Size (Fractional in) | Actual Size (Decimal in) | Metric (Actual / Nominal mm) | Min Face Shell / Web (ASTM C90) | Core Fill / Block | Blocks / 100 sq ft | Primary Structural Application |
|---|---|---|---|---|---|---|---|
| 4" × 8" × 16" | 3-5/8" × 7-5/8" × 15-5/8" | 3.625" × 7.625" × 15.625" | 90 × 190 × 390 mm | 0.75" / 0.75" | 0.08 cu ft (138 in³) | 112.5 | Interior non-load-bearing partitions, fire separation walls, masonry veneer & utility enclosures |
| 6" × 8" × 16" | 5-5/8" × 7-5/8" × 15-5/8" | 5.625" × 7.625" × 15.625" | 140 × 190 × 390 mm | 1" / 0.75" | 0.18 cu ft (311 in³) | 112.5 | Light exterior walls, residential garage walls, tall interior partitions & property screen fences |
| 8" × 8" × 16" | 7-5/8" × 7-5/8" × 15-5/8" | 7.625" × 7.625" × 15.625" | 190 × 190 × 390 mm | 1.25" / 0.75" | 0.28 cu ft (484 in³) | 112.5 | Standard load-bearing residential & commercial walls, single-story structures & structural stems |
| 10" × 8" × 16" | 9-5/8" × 7-5/8" × 15-5/8" | 9.625" × 7.625" × 15.625" | 240 × 190 × 390 mm | 1.375" / 1" | 0.38 cu ft (657 in³) | 112.5 | High-wind load bearing walls, multi-story commercial masonry & shallow basement walls |
| 12" × 8" × 16" | 11-5/8" × 7-5/8" × 15-5/8" | 11.625" × 7.625" × 15.625" | 290 × 190 × 390 mm | 1.5" / 1" | 0.49 cu ft (847 in³) | 112.5 | Below-grade basement foundations, deep retaining stems, warehouse firewalls & heavy axial loads |
Why does an 8×8×16 concrete block actually measure 7-5/8" × 7-5/8" × 15-5/8"? Masonry design follows modular coordination so that blocks plus mortar joints land on clean 8-inch and 16-inch grid lines.
Actual Block + One 3/8" Mortar Joint
Nominal dimensions represent the space a concrete block occupies in the finished wall, including one 3/8" (0.375") horizontal bed joint and one 3/8" vertical head joint. Architects and estimators use nominal dimensions (8" × 16" face = 0.889 sq ft, or 1.125 blocks per sq ft) to lay out wall lengths, window openings, and course heights.
Nominal Size − 3/8" (0.375")
Specified (actual) dimensions are the physical factory measurements of an unlaid block in the lumberyard: 7.625" wide × 7.625" high × 15.625" long. Under ASTM C90, permissible manufacturing variation is ±1/8" (3.2 mm) from these specified dimensions.
200 × 200 × 400 mm Nominal − 10 mm Joint
In metric masonry specifications, the standard 8×8×16 CMU corresponds to a 200 × 200 × 400 mm nominal module with a 10 mm mortar joint, yielding an actual block size of 190 × 190 × 390 mm (12.5 blocks per square meter).
No—all three terms refer to the exact same modular dimensions (7-5/8" × 7-5/8" × 15-5/8" actual for a standard 8×8×16 unit). Historically, "cinder block" described lightweight units made with coal cinders, whereas modern "concrete blocks" or "CMUs" (Concrete Masonry Units) use Portland cement paired with expanded shale, clay, slate (lightweight), or crushed stone/sand aggregate (normal weight) under ASTM C90.
Beyond standard two-core stretchers, masonry walls require specialized modular units to turn corners, finish door and window jambs, embed horizontal rebar, and create textured architectural facades.
Nominal: 8" × 8" × 16" • Actual Bed: 7-5/8" × 7-5/8" × 15-5/8" (+1/2" to 3/4" rough face projection)
Split-face blocks are cast as a double unit and mechanically split down the middle to expose a rough, stone-like aggregate texture. While the mortar bed and height match standard ASTM C90 dimensions (7-5/8" × 15-5/8"), the fractured face projects 1/2" to 3/4" past the mortar line.
Nominal: 8" × 8" × 8" • Actual: 7-5/8" × 7-5/8" × 7-5/8" (190 × 190 × 190 mm)
Half-length blocks eliminate wet-saw cutting at vertical wall ends, control joints, and window/door rough openings in running-bond walls. Each half block covers 0.444 sq ft of wall face (2.25 units per sq ft).
Nominal: 8" × 4" × 16" • Actual: 7-5/8" × 3-5/8" × 15-5/8" (190 × 90 × 390 mm)
Half-height CMUs lay 3 courses per vertical foot instead of 1.5 courses, requiring 225 blocks per 100 sq ft. They are widely used for coursed ashlar architectural bands and fine-increment foundation stem height adjustments.
Nominal: 8" × 8" × 16" • Channel Clear Opening: ~3-1/2" to 4-1/2" wide × 4-1/2" deep
Bond beam units feature depressed or knock-out webs that form a continuous horizontal trough for #4–#6 reinforcing bars and structural grout over openings and at top-of-wall bond courses.
Searching for retaining wall block sizes? Dry-stack segmental retaining wall (SRW) blocks use interlocking rear lips or pins with zero mortar joints, so their nominal and actual face dimensions are identical—unlike mortared ASTM C90 cinder blocks.
| Retaining Wall Block Class | Typical Dimensions (H × W × Depth) | Exposed Face Area | Blocks / 100 sq ft | Typical Gravity Wall Limit |
|---|---|---|---|---|
| Small Garden / Planter Wall Block | 4" H × 12" W × 8" D (102 × 305 × 203 mm) | 0.333 sq ft | 300 blocks | Up to 2.0 – 2.5 ft |
| Medium Landscape Retaining Block | 6" H × 16" W × 12" D (152 × 406 × 305 mm) | 0.667 sq ft | 150 blocks | Up to 3.0 – 4.0 ft |
| Large Commercial SRW Block | 8" H × 18" W × 12" D (203 × 457 × 305 mm) | 1.000 sq ft | 100 blocks | 4.0+ ft (with geogrid) |
| Mortared Structural CMU (8×8×16) | 7-5/8" H × 15-5/8" L × 7-5/8"–11-5/8" D | 0.889 sq ft (with 3/8" joint) | 112.5 blocks | Engineered rebar + footing |
Planning a dry-stack landscape or segmental retaining wall? Calculate courses, cap blocks, and crushed stone backfill with our specialized calculator:
Open Retaining Wall Block Calculator →Once you confirm your concrete block size, every downstream masonry takeoff—block quantity, mortar bags, core grout volume, and installed wall cost—scales directly from those dimensions:
1.125 blocks / sq ft (8×16 face)
Deduct doors, windows, and custom openings across multiple walls with waste allowance.
Concrete Block Calculator →
~13 blocks per 80-lb bag (3/8" joint)
Calculate whole 60-lb or 80-lb pre-mix mortar bags for bed and head joints.
Block Mortar Calculator →
0.08 to 0.49 cu ft / block (4"–12" CMU)
Core volume triples from 6" to 12" blocks. Estimate cubic yards or 80-lb bags for grouted cells.
Concrete Block Fill Calculator →
Material + Mason Labor per sq ft
Price complete concrete block walls, foundations, and fences including blocks, mortar, reinforcement, and labor.
Block Wall Cost Calculator →
All concrete block dimensions, minimum face-shell/web thicknesses, and modular coordination rules on this page are verified against North American masonry standards:
Field note: Always verify specified dimensions and core geometry with your local block producer before fabricating steel lintels or setting tight rough opening frames.