ft
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ft
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ft²
Total area of doors and windows
Standard 8×8×16 is most common
$
Typical: $1.50–$3.50 per block
Concrete Blocks Needed
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How to Calculate Concrete Blocks
Standard concrete masonry units (CMU) are 8 inches high × 16 inches long with a 3/8-inch mortar joint. The nominal size including mortar is 8×16 inches = 0.888 square feet per block. To find block count, divide net wall area by the area per block, then add waste.
Block Formula
Wall Area = Length × Height − Openings
Blocks = Wall Area ÷ Area per Block × (1 + Waste%)
Example: 20 ft × 6 ft = 120 ft². No openings. 120 ÷ 0.888 = 135 blocks + 10% waste = 149 blocks. Mortar: approximately 1 bag (70 lb) of mortar per 30–35 blocks.
💡 Pro tip: Standard CMU walls require 3/8-inch mortar joints. A 90 lb bag of mortar covers approximately 30 standard 8×8×16 blocks. For a retaining wall, add rebar every 4 feet horizontally and at corners.
Frequently Asked Questions
A standard CMU block wall costs $10–$20 per square foot installed, including materials and labor. A simple 20×6 ft wall (120 ft²) typically costs $1,200–$2,400. Decorative split-face block, reinforced retaining walls, and walls requiring footings are more expensive. DIY block laying saves 50–60% on labor.
A standard pallet of 8×8×16 concrete blocks contains 90 blocks. Knowing this helps you calculate delivery needs — for large jobs, order in full pallets to minimize per-block cost and avoid partial pallet fees. Most suppliers require a minimum delivery of 1 pallet.
For structural walls (house foundations, load-bearing walls) and retaining walls over 3 feet, a concrete footing is required — typically twice the wall width and as deep as the frost line. For decorative garden walls under 3 feet, a gravel base or minimal footing may suffice. Always check local building codes.
CMU (Concrete Masonry Unit) is made with Portland cement and aggregates — it's the modern standard. Cinder blocks were originally made with fly ash (a coal combustion byproduct) as aggregate. True cinder blocks are no longer widely produced. The terms are often used interchangeably, but modern "cinder blocks" are actually CMU. CMU is stronger and more uniform.
Type S mortar (1,800 psi) is the standard for exterior and below-grade block work. Type M (2,500 psi) is for heavy structural loads. Type N (750 psi) is only for non-structural above-grade interior use. Joints should be 3/8 inch thick. Use bagged Type S premix for smaller projects — it's convenient and reliably proportioned.
Standard CMU walls: $10–$20/ft² installed. Reinforced retaining walls: $15–$30/ft². Materials alone: $3–$6/ft². Labor accounts for 50–65%. DIY is achievable for garden walls under 3 ft — structural and retaining walls should be professionally built and permitted due to the safety and structural implications.
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