Concrete masonry units (CMU), commonly called concrete blocks or cinder blocks, are standardized building materials used for structural and non-structural construction. The most common size is the 8×8×16 block (nominal dimensions), which measures 7⅝" × 7⅝" × 15⅝" actual size to accommodate ⅜" mortar joints. This guide covers standard CMU dimensions, hollow vs solid blocks, specialty sizes, and quantity calculations for construction projects.
| Nominal Size | Actual Dimensions | Weight (Hollow) | Weight (Solid) | Blocks per SF |
|---|---|---|---|---|
| 4×8×16" | 3⅝" × 7⅝" × 15⅝" (92 × 194 × 397 mm) |
22-26 lbs (10-12 kg) |
32-36 lbs (15-16 kg) |
2.25 blocks |
| 6×8×16" | 5⅝" × 7⅝" × 15⅝" (143 × 194 × 397 mm) |
28-32 lbs (13-15 kg) |
45-50 lbs (20-23 kg) |
2.25 blocks |
| 8×8×16" (Most Common) |
7⅝" × 7⅝" × 15⅝" (194 × 194 × 397 mm) |
32-38 lbs (15-17 kg) |
54-60 lbs (25-27 kg) |
1.125 blocks |
| 10×8×16" | 9⅝" × 7⅝" × 15⅝" (244 × 194 × 397 mm) |
38-42 lbs (17-19 kg) |
65-72 lbs (29-33 kg) |
1.125 blocks |
| 12×8×16" | 11⅝" × 7⅝" × 15⅝" (295 × 194 × 397 mm) |
44-50 lbs (20-23 kg) |
75-85 lbs (34-39 kg) |
1.125 blocks |
| 8×4×16" (Half-height) |
7⅝" × 3⅝" × 15⅝" (194 × 92 × 397 mm) |
18-22 lbs (8-10 kg) |
30-35 lbs (14-16 kg) |
2.25 blocks |
| 8×2×16" (Cap/Lintel) |
7⅝" × 1⅝" × 15⅝" (194 × 41 × 397 mm) |
10-12 lbs (5-6 kg) |
18-20 lbs (8-9 kg) |
4.5 blocks |
| Block Type | Description | Core Configuration | Typical Weight (8×8×16) | Applications |
|---|---|---|---|---|
| 2-Core Hollow | Two rectangular voids (most common) | 2 cores, 55-60% void space | 32-36 lbs | Standard walls, foundations, non-load-bearing |
| 3-Core Hollow | Three rectangular voids | 3 cores, 50-55% void space | 35-38 lbs | Load-bearing walls, structural applications |
| Solid Block | No voids or minimal cores (<25% void) | Solid or small cores | 54-60 lbs | Below-grade construction, high-load areas, piers |
| Open-End Block | One or both ends open (no end webs) | Continuous vertical cores | 30-34 lbs | Vertical rebar/conduit placement, grouted cores |
| Lintel Block | U-shaped, open top for rebar/concrete | U-channel configuration | 28-32 lbs | Above windows/doors, beam construction |
| Bond Beam Block | Depressed webs for horizontal rebar | Channels for rebar placement | 32-36 lbs | Top courses, seismic reinforcement, tie beams |
| Cap Block | Solid top surface (decorative finish) | Cores bottom, solid top 2" | 38-42 lbs | Wall tops, parapet caps, decorative finishes |
| Corner/Return Block | Flat end for exposed corners | One smooth end face | 34-38 lbs | Wall corners, pilasters, decorative ends |
| Sash Block | Vertical slot for window frames | Grooved end for window installation | 32-36 lbs | Window/door jambs |
| Split-Face Block | Fractured face for texture | Standard cores, textured face | 34-38 lbs | Decorative walls, exterior finishes |
| Type | Aggregate Used | Density | Weight (8×8×16 hollow) | Compressive Strength | Applications |
|---|---|---|---|---|---|
| Lightweight | Expanded shale, clay, slate, or pumice | Less than 105 lb/cu ft | 24-28 lbs (11-13 kg) |
1,900-2,500 psi | Non-load-bearing walls, upper floors, ease of handling |
| Medium Weight | Combination aggregates, coal cinders | 105-125 lb/cu ft | 32-38 lbs (15-17 kg) |
2,500-3,500 psi | General construction, most common, balanced properties |
| Normal Weight | Sand, gravel, crushed stone | 125+ lb/cu ft | 40-48 lbs (18-22 kg) |
3,000-4,000+ psi | Load-bearing walls, foundations, high-strength requirements |
Nominal size: Design dimensions including one mortar joint (typically ⅜" or 10mm). Example: 8×8×16" nominal. Used for architectural drawings and modular coordination. Actual size: Physical manufactured dimensions of the block itself. Example: 7⅝" × 7⅝" × 15⅝" actual (⅜" less than nominal on each dimension). Used for ordering, material estimation, and construction. Why the difference? Mortar joint (⅜") added to actual dimension = nominal dimension. Allows modular coordination in 4" increments (4", 8", 12", 16"). Ensures standard door/window openings fit without cutting blocks.
Width × Height × Length: Standard naming order for CMUs. Example: 8×8×16 block: 8" wide (wall thickness), 8" high (vertical dimension), 16" long (horizontal along wall). Width: Determines wall thickness (4", 6", 8", 10", 12"). Height: Typically 8" (can be 4", 2" for specialty blocks). Length: Almost always 16" (modular standard for construction industry).
CMU dimensions based on 4-inch module (4", 8", 12", 16", etc.). Standard 8×8×16 block: 8" high (two courses = 16" vertical), 16" long (standard module). Advantages: Standard door openings (36") = 27 blocks long (2.25 blocks × 12 courses). Standard window openings align with block coursing. Reduces cutting and waste. Design principle: Buildings designed in 8" increments horizontally and 8" increments vertically for efficient block usage.
Nominal dimensions: 8" × 8" × 16" (203 × 203 × 406 mm). Actual dimensions: 7⅝" × 7⅝" × 15⅝" (194 × 194 × 397 mm). Weight (hollow 2-core): 32-38 lbs (15-17 kg). Weight (solid): 54-60 lbs (25-27 kg). Coverage: 1.125 blocks per square foot (9 blocks per 8 square feet). Compressive strength: 1,900-3,500+ psi depending on aggregate and quality. Core configuration: Two rectangular cores, 55-60% void space. Web thickness: 1-1.25" between cores and on ends. Face shell thickness: 1-1.5" top and bottom.
Historical development: Standardized in 1920s-1930s for modular construction. Perfect proportions: 2:1 length-to-height ratio (16" long, 8" high). One-hand carry: At 35 lbs average, manageable for skilled masons (though two hands recommended). Modular efficiency: 8" and 16" fit building standards (door/window openings, floor heights). Economic sweet spot: Large enough for fast construction, small enough for reasonable weight and material cost. Industry adoption: 95%+ of CMU construction uses 8×8×16 or variations (4×8×16, 6×8×16, 12×8×16).
Foundation walls: Below-grade residential and commercial construction. Structural walls: Load-bearing exterior and interior walls. Basement walls: Below-grade construction with waterproofing. Retaining walls: Earth retention, landscaping (under 4 feet typically). Partition walls: Interior non-load-bearing divisions. Commercial buildings: Warehouses, schools, industrial facilities. Fire walls: Fire-rated separations between buildings or spaces.
Actual size: 3⅝" × 7⅝" × 15⅝". Weight (hollow): 22-26 lbs. Applications: Non-load-bearing partition walls, interior divisions, veneer walls (with structural backup), garden walls (under 3 feet), decorative screening. Advantages: Lightweight, economical (less material), narrow walls (maximize interior space). Limitations: Not suitable for load-bearing or below-grade use, lower insulation value than thicker blocks.
Actual size: 5⅝" × 7⅝" × 15⅝". Weight (hollow): 28-32 lbs. Applications: Light load-bearing walls, above-grade residential walls, interior structural partitions, low retaining walls. Advantages: Balance of strength and weight, moderate cost, suitable for single-story residential. Common in: Arizona, New Mexico, Southern California (residential construction standard in some areas).
Actual size: 7⅝" × 7⅝" × 15⅝". Weight (hollow): 32-38 lbs. Applications: Foundation walls, basement walls, load-bearing walls (up to 3-4 stories with reinforcement), retaining walls (under 6-8 feet), commercial construction, most versatile size. Advantages: Standard thickness for residential construction, excellent strength-to-weight ratio, widely available, optimal for insulation (cores filled with foam or grout). Industry standard: Default choice unless project has specific requirements for different width.
Actual size: 9⅝" × 7⅝" × 15⅝". Weight (hollow): 38-42 lbs. Applications: Tall load-bearing walls (multi-story buildings), high wind/seismic zones, heavy equipment foundations, commercial/industrial buildings. Advantages: Increased wall thickness for added strength, better insulation capacity (more core space for insulation), increased fire resistance. Considerations: Higher material cost, heavier (more labor intensive), requires wider foundation footing.
Actual size: 11⅝" × 7⅝" × 15⅝". Weight (hollow): 44-50 lbs. Applications: Heavy-duty load-bearing walls, below-grade walls with high earth pressure, commercial buildings over 4 stories, retaining walls over 8 feet, fire-rated assemblies (2-4 hour ratings). Advantages: Maximum strength and load capacity, excellent insulation potential, highest fire resistance. Disadvantages: Expensive, very heavy (challenging to handle), requires substantial foundation support, overkill for most residential applications.
Actual size: 7⅝" × 3⅝" × 15⅝". Nominal height: 4" (half of standard 8"). Weight (hollow): 18-22 lbs. Applications: Finishing top courses (when wall height requires half-block), below window sills, decorative banding, bond beam courses (when 4" height needed). Coverage: 2.25 blocks per square foot (same as 4×8×16 blocks). Advantage: Maintains modular coordination for odd wall heights.
Typical sizes: 4×2×16, 8×2×16, 12×2×16 (2" nominal height). Actual height: 1⅝". Configuration: Solid top surface (no cores visible), cores or solid bottom. Weight (8×2×16): 10-15 lbs. Applications: Top course of walls (finished appearance), parapet caps, planter walls, fence tops. Finish options: Smooth face, split-face texture, colored concrete, beveled edges. Purpose: Weatherproofing (prevents water entering cores), decorative finish, protects wall top from erosion.
Configuration: U-shaped channel (open top, solid bottom). Standard sizes: 6×8×16, 8×8×16, 10×8×16, 12×8×16 (all U-shaped). Purpose: Creates horizontal beam above windows and doors. Installation: Place inverted over opening, fill U-channel with concrete and rebar (creates reinforced lintel). Load capacity: Depends on rebar size and quantity (typically #4 or #5 rebar, 2-4 bars). Advantages: Integral to wall system, faster than poured-in-place lintel, modular dimensions.
Configuration: Standard block with notched/depressed webs for horizontal rebar. Purpose: Horizontal reinforcement at top of wall, intermediate courses (seismic zones). Installation: Lay horizontally, place rebar in channels, fill cores with grout. Typical placement: Every 4-8 feet vertically (building code dependent), top course of walls, openings (above/below windows). Seismic requirement: Mandatory in high-seismic zones at specified intervals.
8×8×16 blocks: 1.125 blocks per SF = 113 blocks per 100 SF of wall. 4×8×16 or 8×4×16 blocks: 2.25 blocks per SF = 225 blocks per 100 SF. 12×8×16 blocks: 1.125 blocks per SF (same as 8×8×16—same height and length). For linear walls: 1.5 blocks per linear foot (standard 8×8×16 blocks, single wythe wall). Example calculation: 20 ft long × 8 ft tall wall = 160 SF. 160 × 1.125 = 180 blocks. Add 5% waste: 180 × 1.05 = 189 blocks (order 190-200).
Windows and doors: Calculate opening area, subtract from total wall area. Standard door (36" × 80"): 20 SF = 22-23 fewer blocks. Standard window (36" × 48"): 12 SF = 13-14 fewer blocks. Partial blocks: Openings rarely align perfectly with block modules—may require cutting. Add 3-5% extra for cut blocks around openings.
Configuration: 2 or 3 rectangular cores running vertically through block. Void space: 50-60% of total volume. Weight (8×8×16): 32-38 lbs. Advantages: Lighter weight (easier handling, less labor cost), lower material cost, cores allow vertical rebar placement, cores allow insulation (foam, grout, perlite), better insulation value when cores filled. Applications: 90% of CMU construction (standard for most projects), foundation walls, above-grade walls, reinforced masonry. Compressive strength: 1,900-3,500 psi (adequate for most residential/commercial construction).
Configuration: Little to no voids (less than 25% void space per ASTM standards). Weight (8×8×16): 54-60 lbs (70-80% heavier than hollow). Advantages: Higher compressive strength (3,500-5,000+ psi), better sound insulation (dense mass blocks sound), enhanced fire resistance, superior durability below-grade. Disadvantages: Very heavy (difficult handling, higher labor cost), more expensive (70% more concrete), no rebar or insulation capability, poor thermal insulation. Applications: Below-grade foundations (high earth pressure), piers and columns, high-load areas (elevator shafts, stairwells), retaining walls over 6 feet, historically significant restoration.
Configuration: Hollow blocks with cores filled with concrete grout. Grout composition: Portland cement, sand, pea gravel (fine aggregate), water. Fully grouted: All cores filled (creates solid block strength). Partially grouted: Selected cores filled (typically every 4-8 feet or at openings). Purpose: Reinforcement (combines with vertical rebar), increased strength (approaching solid block), improved fire rating, earthquake resistance (required in seismic zones). Weight (fully grouted 8×8×16): 60-70 lbs. Applications: Load-bearing walls, seismic zones, tall walls (over 10 feet), retaining walls.
Grade N (Normal): 1,900 psi minimum compressive strength. For general above-grade use, non-load-bearing or light load-bearing. Grade S (Structural): 2,500 psi minimum compressive strength. For load-bearing applications, structural masonry. High-Strength (Premium): 3,000-5,000+ psi. For heavy-duty structural, seismic zones, commercial buildings. Testing standard: ASTM C90 (Standard Specification for Loadbearing Concrete Masonry Units).
Aggregate type: Normal weight (sand/gravel) > medium weight > lightweight (expanded shale). Cement content: Higher cement = higher strength and cost. Core configuration: Solid blocks stronger than hollow (less void space). Curing process: Steam-cured blocks reach full strength faster. Age: Concrete gains strength over time (28-day standard for testing). Moisture content: Dry blocks have higher compressive strength than saturated blocks. Quality control: Reputable manufacturers maintain consistent strength through batch testing.
Grade N (Normal): For above-grade use, minimal freeze-thaw exposure. Grade S (Severe): For below-grade, high moisture, freeze-thaw exposure. Lower water absorption requirement (<175 lb/cu ft, 18% max water absorption for medium weight). More durable in harsh conditions. Selection guide: Use Grade N for interior walls, above-grade in mild climates. Use Grade S for foundations, below-grade, cold climates with freeze-thaw cycles, exterior walls exposed to weather.
1. Mixing: Portland cement, aggregates (sand/gravel/lightweight), water mixed in batch plant. 2. Molding: Mix placed in block molds, compressed with high pressure (1,500+ psi) and vibration. Creates dense, uniform blocks. 3. Curing: Low-pressure steam curing (12-24 hours, accelerated strength) or ambient air curing (28 days, traditional). 4. Quality control: Random sampling for strength testing, dimension verification. 5. Packaging: Stacked on wood pallets, shrink-wrapped or banded. 6. Delivery: Pallets delivered via flatbed truck, unloaded with forklift/crane.
Blocks per cube (pallet): 8×8×16 hollow: 90-108 blocks per pallet (varies by manufacturer). 4×8×16 hollow: 180-200 blocks per pallet. Weight per cube: 8×8×16: 3,000-4,000 lbs per pallet. Pallet dimensions: 48" × 48" standard wood pallet. Stacking: 6-9 layers high, alternating orientation for stability. Delivery considerations: Forklift or crane required, pallets placed near work area, tarps recommended (protect from rain before installation).
Mortar type: Type N (general purpose, 750 psi), Type S (structural, below-grade, 1,800 psi), Type M (heavy load, 2,500 psi). Joint thickness: ⅜" standard (horizontal and vertical joints). Bed joint: Horizontal mortar layer between courses. Head joint: Vertical mortar between blocks in same course. Face shell bedding: Mortar applied to outer edges only (hollow blocks), saves mortar, adequate for most applications. Full bedding: Mortar covers entire block surface (required for solid blocks or high-load areas).
Vertical rebar: Placed in cores, cores grouted, provides tensile strength. Typical: #4 or #5 rebar every 4-8 feet horizontally. Horizontal rebar: Placed in bond beam blocks, provides lateral strength, resists wall rotation. Required in seismic zones. Ladder reinforcement: Wire ladder-style reinforcement laid in bed joints every 2-3 courses. Prevents shrinkage cracks, ties multiple wythes together. Seismic requirements: High-seismic zones require extensive reinforcement (vertical and horizontal rebar, fully grouted cores, bond beams every 4-8 feet).
Cold weather (below 40°F): Heat sand and water for mortar, protect fresh work with insulated blankets 48 hours, avoid freezing (destroys bond). Hot weather (above 90°F): Wet blocks before laying (prevent rapid mortar water loss), shade work area, mist walls during curing. Rain: Cover fresh work immediately (rain washes mortar before set), don't lay blocks during heavy rain. Ideal conditions: 50-80°F, low wind, overcast.
8×8×16 hollow (standard gray): $1.75-$3.50 per block. 8×8×16 solid: $3.00-$5.00 per block (70-100% more expensive). Lightweight blocks: $2.25-$4.00 per block (premium over normal weight). Colored blocks: $3.00-$6.00 per block (buff, red, brown, charcoal). Split-face decorative: $3.50-$7.00 per block. Specialty blocks (lintel, bond beam, corner): $4.00-$8.00 per block. Regional variation: 20-30% price difference between high-cost (Northeast, West Coast) and low-cost (Southeast, Midwest) regions.
Average mason rate: $30-$60 per hour (varies by region and experience). Block laying speed: 75-150 blocks per day (experienced mason, standard wall, good conditions). Installation cost per SF: $8-$18 per square foot installed (includes labor and mortar, excludes blocks). Total cost per SF: $12-$25 per square foot (materials + labor). Additional costs: Rebar and grouting: add $2-$5 per SF. Scaffolding (walls over 8 feet): $1-$3 per SF. Waterproofing (below-grade): $1-$4 per SF. Surface finish (stucco, parge coat): $2-$8 per SF.
CMU advantages: Faster installation (no formwork or curing wait), lower cost for small projects, better insulation (hollow cores), easier to work with (cut, modify). Poured concrete advantages: Higher strength (4,000-6,000 psi), seamless monolithic structure, better for complex shapes, required for walls over 10-12 feet. Cost comparison: CMU: $12-$25 per SF. Poured concrete: $15-$35 per SF (includes formwork, rebar, pouring, finishing).
CMU advantages: Fire-proof (concrete doesn't burn), termite-proof, rot-proof (no moisture damage), higher sound insulation, lower insurance premiums, 100+ year lifespan. Wood framing advantages: Lower cost ($8-$15 per SF vs $12-$25 for CMU), faster installation, easier electrical/plumbing runs, better insulation (R-19 fiberglass vs R-4 for uninsulated CMU). Regional trends: Southwest, Florida: CMU dominates residential construction. Northeast, Midwest, Northwest: Wood framing dominates.
CMU advantages: Faster installation (larger units), lower cost ($12-$25 per SF vs $20-$40 for brick), structural (load-bearing without backup wall). Brick advantages: Superior aesthetics (traditional, high-end appearance), better durability (100+ years vs 75-100 for CMU), lower maintenance (brick doesn't need painting). Combination: CMU structural wall + brick veneer (common for commercial buildings)—combines CMU economy with brick aesthetics.
Answer: "Cinder blocks" is outdated terminology for blocks made with coal cinders (ash) as aggregate, common 1940s-1970s. Modern "concrete blocks" use sand, gravel, or lightweight aggregates. Cinder blocks weaker and less durable—rarely manufactured today. Terms often used interchangeably, but technically different. Always specify "concrete masonry units" (CMU) for modern construction.
Answer: 1.125 blocks per SF × 100 SF = 112.5 blocks. Round up to 113 blocks. Add 5% waste: 113 × 1.05 = 119 blocks (order 120 blocks or 2 pallets if pallets contain 90 blocks).
Yes, with proper preparation: Use Grade S blocks (severe weather rating, lower water absorption), apply waterproofing membrane on exterior face (tar, rubberized coating, or plastic sheeting), install drainage system (perforated pipe at footing level), consider solid blocks for below-grade (better resistance to earth pressure). CMU foundation walls standard in residential construction.
Not always: Hollow blocks adequate for non-load-bearing or light load-bearing walls. Fill cores when: Load-bearing structural walls require added strength, vertical rebar installed (rebar must be grouted in place), seismic or high-wind zones (building code requirement), retaining walls over 4 feet, piers or columns supporting heavy loads. Partially grouted (every 4-8 feet) often sufficient—fully grouted only when required by code or engineer.
Uninsulated hollow 8×8×16 CMU: R-2 to R-4 (very poor insulation). Cores filled with foam insulation: R-10 to R-13. Exterior rigid foam (2" XPS): Add R-10 = total R-15 to R-20. Furred interior wall with fiberglass: Add R-11 to R-13 = total R-15 to R-17. Code requirements: Modern energy codes require R-10 to R-20 depending on climate zone—uninsulated CMU no longer meets code in most areas.
Expected lifespan: 75-100+ years with proper installation and maintenance. Factors affecting longevity: Quality of blocks (Grade S lasts longer than Grade N), proper waterproofing (especially below-grade), adequate drainage (prevents water damage), climate (freeze-thaw cycles shorten life), maintenance (repoint mortar joints every 25-30 years). Properly maintained CMU buildings can last 100+ years (many 1920s-1940s CMU structures still in use).