Cinder Block Calculator

Concrete Masonry Engineering & ASTM C90 Standards (NCMA)

Concrete masonry wall construction relies on standardized modular dimensions:

• **

• Standard 8 × 8 × 16 CMU Geometry**:

• Actual Dimensions: 7(5) / (8)" Height × 7(5) / (8)" Width × 15(5) / (8)" Length

• Nominal Modular Dimensions: 8" × 8" × 16"

• Face Area per Block: (8 × 16) / (144) = (128) / (144) = 0.8889 sq ft

• Block Density Constant: (1) / (0.8889) = 1.125 blocks per square foot

• **

• Core Block & Mortar Formulas**:

Exact Blocks = Net Wall Area (sq ft) × 1.125

Total Blocks = Exact Blocks ×

Mortar Bags (80 lb) = Total Blocks33

Vertical Courses = Wall Height (inches)8" = Height (ft) × 1.5

• **

• Standard Project Benchmarks**:

• 20 × 2 ft Garden Bed (40 sq ft): 48 Blocks | 2 Mortar Bags | 3 Courses

• 40 × 4 ft Retaining Wall (160 sq ft): 198 Blocks | 6 Mortar Bags | 6 Courses

• 30 × 8 ft Garage Wall (240 sq ft): 297 Blocks | 9 Mortar Bags | 12 Courses

• 100 × 8 ft Basement (800 sq ft): 990 Blocks | 30 Mortar Bags | 12 Courses

How to Use This Calculator

Enter your Wall Length (e.g. 30 in ft), Wall Height (e.g. 8 in ft), CMU Block Size (Nominal H × W × L) — choose from 8" × 8" × 16" Standard CMU (1.125 blocks / sq ft - Most Common), 6" × 8" × 16" Partition CMU (1.125 blocks / sq ft), 4" × 8" × 16" Veneer / Screen CMU (1.125 blocks / sq ft), Doors & Windows Deduction Area (e.g. 0 in sq ft), Cutting & Breakage Waste Allowance — choose from 0% (Exact Theoretical Count), 5% (Experienced Mason / Straight Wall), 10% (Recommended - Corners, Cuts & Breakage), Concrete Core-Fill Grouting — choose from Hollow / No Core Grout (Standard Non-Load Bearing), Reinforced 32" O.C. (Fill Every 2nd Core - Rebar Columns), Solid Fill (100% Core Grout - Retaining Wall / Foundation), and Masonry Project Benchmark — choose from Custom Wall Dimensions, 30 × 8 ft Garage Foundation Wall → 297 Blocks (270 Exact) / 9 Mortar Bags, 40 × 4 ft Landscape Retaining Wall → 198 Blocks (180 Exact) / 6 Mortar Bags. Measure twice before entering dimensions — small measurement errors scale up significantly in material estimates.

The Formula

Nominal 8x16 face = (8*16)/144 = 0.888889 sq ft => 1.125 blocks per sq ft

Worked Example

A mason building a 30 × 8 ft garage foundation wall calculates the net wall area as 240 sq ft × 1.125 = 270 cinder blocks exact, adding 10% waste to purchase 297 blocks and 9 bags of mortar.

Understanding Your Result

Standard modular brick (3⅝" × 2¼" × 7⅝") with 3/8" mortar joint: approximately 6.75 bricks per sq ft of single-wythe wall. Add 5–10% waste factor for cuts and breakage. Mortar consumption: 1 bag of Type S mortar covers approximately 10–12 sq ft of brick surface. CMU (concrete masonry unit) 8×8×16 blocks: approximately 1.125 blocks per sq ft plus 5% waste. Always verify local building code requirements for wall thickness in structural or load-bearing applications.