Free concrete block calculator to estimate CMU blocks, mortar bags, and sand needed for walls. Includes cost estimates for retaining walls, foundations, and block fences.
Most common size for walls and foundations
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Planning a block wall, retaining wall, or foundation? Our concrete block calculator (also called CMU or cinder block calculator) determines exactly how many blocks you need, plus mortar bags and sand quantities. Get accurate material estimates with cost projections before you start building.
Concrete blocks (CMU - Concrete Masonry Units) are measured by their nominal dimensions. Standard blocks are 8" × 8" × 16" (actual: 7-5/8" × 7-5/8" × 15-5/8") to account for mortar joints. You need approximately 1.125 blocks per square foot of wall area. Mortar requirements average 3 bags (80 lb) per 100 blocks, and sand is needed at about 1 ton per 7-8 bags of mortar.
Block Calculation Formula
Blocks = Wall Area (sq ft) × 1.125 × (1 + Waste %)Know exactly how many blocks to order—avoid shortages or excess.
Calculate supplementary materials needed for complete installation.
Account for breakage, cuts, and installation waste automatically.
Budget your project with accurate material cost estimates.
Calculate for standard 8", 4" partition, or 12" foundation blocks.
Build decorative garden walls or retaining walls for landscaping projects.
Calculate blocks for basement or crawl space foundation walls.
Estimate materials for detached garage or workshop block walls.
Build durable block privacy fences that last for decades.
Create solid block foundations for sheds and outbuildings.
Use 4" partition blocks for interior non-load-bearing walls.
For standard 8×8×16 inch blocks with 3/8" mortar joints, you need approximately 1.125 blocks per square foot of wall area. This accounts for the mortar joints reducing the effective block size.