ConcreteCalc
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Concrete Block (CMU) Calculator

Calculate the number of standard cinder / concrete masonry units (8x8x16 CMU blocks), pre-blended masonry mortar bags, and core grout fill volume for concrete block walls and foundations. Includes waste allowances for cutting corners and openings.

Interactive Block Calculator

ENGINEERING SCHEMATIC
Standard 8×8×16 Concrete Masonry Unit (CMU)
Volume (V) = Area × Depth 1 Cubic Yard = 27 Cubic Feet
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Pro Contractor Recommendation: Requires 112.5 blocks per 100 sq ft of wall area. For core fill, every 100 blocks requires approximately 0.45 cu.yds of pea gravel grout.
Example default values loaded
Wall Dimensions
Block Size & Core Grout Filling
%
Total Concrete Blocks (CMU)
189 blocks
Includes 5% cutting & breakage allowance
Mortar Bags
6 bags
Standard Type S/N bags (~33 blocks/bag)
Core Grout Volume
1.61 cu yd
43.5 cu ft (1.23 m³)
Wall Face Area
160.0 sq ft
(14.9 m²)

How Many Concrete Blocks Do I Need Per Square Foot?

A standard American concrete masonry unit (CMU) has nominal dimensions of 8" high × 8" wide × 16" long. Its actual manufactured size is 7-5/8" × 7-5/8" × 15-5/8" to accommodate a standard 3/8-inch mortar joint.

One block covers (8 / 12) × (16 / 12) = 0.8889 square feet of wall surface area. Therefore, you need exactly 1.125 blocks per square foot of net wall area (or 112.5 blocks per 100 square feet).

Mortar and Grout Estimations

  • Mortar Bags: A standard 70–80 lb bag of Type S or Type N masonry cement typically lays approximately 30 to 35 standard 8x8x16 blocks.
  • Core Grout: Solid grouting an 8-inch CMU wall requires approximately 0.85 cubic yards of pea-gravel core grout per 100 blocks. For 16" or 24" on-center vertical rebar cells, volume is proportionally reduced.