About this calculator
Count CMU (cinder) blocks for garden walls, foundation walls, garages and extensions, along with the mortar to lay them.
How it’s calculated
A nominal 8×16 block covers 16" × 8" of wall including the ⅜" joint, which works out to 1.125 blocks per sq ft. Blocks = net wall area × blocks per unit area, plus waste.
Worked example
With these inputs:
- Wall length
- 40 ft
- Wall height
- 6 ft
- Openings area
- 0 sq ft
- Block
- 8 × 8 × 16 (standard)
- Blocks per 80 lb mortar bag
- 12
- Waste allowance
- 5%
the result is:
- Blocks needed
- 284 blocks
- Wall area (net)
- 240 sq ft
- Courses
- 9
- Mortar mix bags (80 lb)
- 24 bags @ 12 blocks/bag
Tips from the trade
- Subtract openings, but add back for lintel bearings and cut blocks at the ends.
- Order a few extra half-blocks or cutters for corners and ends.
- Grout-filled cores and bond beams need extra concrete. Work those out with the wall calculator.
Common questions
How many blocks per square foot?
1.125 standard 8×8×16 blocks per sq ft, or 112.5 per 100 sq ft.
Results are estimates for planning and pricing. Check quantities against your drawings, the manufacturer’s data and local building codes before ordering.