Why calculators show net quantities
Block calculators give you the theoretical count for the wall area you enter. On site, corners, partial blocks, broken units, and awkward openings always push the real number higher.
As a starting point, many site engineers allow 5–10% extra blocks on straight runs and more on curved or heavily perforated walls.
Mortar matters too
Wastage is not just blocks — mortar mix loss from spillage, over-mixing, and rework adds cement and sand demand. If gangs are new or the sand is very fine, allow margin on mortar as well.
Use the mortar mix option in the block calculator that matches your spec (e.g. 1:6 for block work) before scaling up for wastage.
Reduce waste with planning
Stack blocks close to the wall line, set out openings before you build, and agree course heights with the carpenter before MEP sleeves go in — that cuts down cut blocks and rejected courses.
Save your net and gross quantities in RazorBuilder so the next phase (plaster, electrical chases) uses the same wall areas.
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