Block Wall (CMU) Calculator
Concrete blocks for walls less openings from your nominal block size, with courses per wall, waste, mortar bags from the product yield and grout for cells.
The block count to order and the mortar and grout to go with it, with the course and per-course arithmetic shown so the wall height and length can be checked against the block module.
Example: A 40 × 8 ft wall with a 3 × 7 ft door is 299 ft² net: 337 blocks of 16 × 8 in nominal, 354 with 5 % waste, 12 courses of 30; 12 bags of mortar at 30 blocks a bag; 88.5 ft³ of grout.
Nominal size includes the joint.
That is what makes the count work.
Block count from area, why the nominal module matters, and where mortar and grout figures come from.
Blocks from area
The wall face area, less doors, windows and other openings, is divided by the face of one block laid — its nominal length times nominal height, which already include the mortar joint. A nominal 16 × 8 in block (actual 15⅝ × 7⅝ in plus a ⅜ in joint) covers exactly 0.889 ft²; a 400 × 200 mm block covers 0.08 m². Nominal sizes and joint thickness differ between countries and block types, so the size is an input with a labelled sample. The result is rounded up to whole blocks and the waste allowance you choose is added for cuts at corners, ends and openings; no waste at all is flagged.
Courses and the module
For each wall the page shows how many courses the height makes and how many blocks a course takes. A height that is not a whole number of courses means a cut course or a change of height, and is flagged. Corner bonding, half blocks, lintel and bond-beam units, and special shapes are not counted separately: they replace standard units in the same area and are usually covered by the waste allowance and your own take-off.
Mortar and grout
Mortar is counted as bags from the yield printed on the mortar product — blocks laid per bag — because that figure depends on the mix, bag size, joint profile and block type; no yield is assumed. Grout for reinforced or filled walls is blocks × the cell volume per block (from the block manufacturer) × the fraction of cells that are filled, given in cubic feet or litres and in cubic yards or cubic metres for ordering. Reinforcing steel, ties and wall structural adequacy are outside the page.
Privacy
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SOURCES
- Nominal versus actual block dimensions: a nominal 16 × 8 in unit is 15 5/8 × 7 5/8 in plus a 3/8 in joint (ASTM C90 sizing convention; sizes and yields are entered, not assumed)
Last reviewed 19 September 2026. How results are checked: How we verify.