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Concrete Block Calculator
Estimate CMU blocks, mortar bags, and corner blocks for a cinder block wall. Supports 4, 6, 8, and 12 in widths plus window and door openings.
Wall and block details
No openings. Add a window or door to subtract its area from the wall.
Blocks you need
93 blocks
- Net wall area
- 80 sq ft
- Openings area
- 0 sq ft
- Working area
- 80 sq ft
- With waste
- 88 sq ft
- Square meters
- 7.43 sq m
- Blocks per sq ft
- 1.05
- Corner blocks (est.)
- 5
- Mortar volume
- 0.96 cu ft
- 80 lb mortar bags
- 3
Frequently Asked Questions about the Concrete Block Calculator
How many concrete blocks do I need per square foot of wall?
About 1.05 blocks per square foot for any standard CMU. All US standard cinder blocks share the same 8 by 16 in face, so the face count is identical regardless of width.
Does the block width change how many blocks I need?
No, not for face count. Width (4, 6, 8, or 12 in) affects wall thickness and load capacity but not the face. The calculator returns the same block count for all four sizes.
How much mortar do I need for a CMU wall?
About 0.012 cubic feet of wet mortar per square foot of wall, per NCMA reference values for standard 3/8 in joints. A typical 80 lb bag of dry mortar mix yields roughly 0.5 cubic feet of wet mortar.
What waste factor should I use for cinder block?
10% is a safe default for a typical residential wall with one or two openings. Drop to 5% for a long straight run with no cuts, and go up to 15% for walls with many corners, angled cuts, or partial blocks.
How many corner blocks should I plan for?
The calculator estimates corner blocks at about 5% of total block count, which covers a typical rectangular wall. For more returns or pilasters, count corners directly (one block per course per corner).