About this calculator
Estimates the take-off for a ceramic hollow block (clay block) wall: full and half/corner block counts from wall area minus openings, and the jointing material (mortar bed or thin-bed glue, your choice) by area coverage.
Formula
wall area = length × height
net area = wall area − Σ opening areas
block footprint = block length × block height
block equivalents = ceil(net area / block footprint)
half blocks = round(block equivalents × half-block %)
full blocks = ceil(block equivalents − half blocks × 0.5)
full/half blocks (incl. waste) = ceil(count × (1 + waste% / 100))
jointing mass = net area × consumption (kg/m²)
jointing bags = ceil(jointing mass / bag size)
Half/corner blocks fill in a course length that isn't an exact multiple of the full block
module — each half block is modelled as covering half a full block's footprint. The fraction
of equivalents supplied as half blocks is a user estimate (half-block %), since it depends
on wall length vs. block module and can't be derived without a real per-course layout.
Worked example
Defaults: 4 m × 2.5 m wall, one 900×2100 mm door opening, 250×238 mm block, 10% half blocks, 7% waste, mortar jointing at 15 kg/m².
wall area = 4000 × 2500 = 10,000,000 mm²
opening area = 900 × 2100 = 1,890,000 mm²
net area = 8,110,000 mm²
block footprint = 250 × 238 = 59,500 mm²
block equivalents = ceil(8,110,000 / 59,500) = 137
half blocks = round(137 × 0.10) = 14; full blocks = ceil(137 − 7) = 130
full blocks incl. waste = ceil(130 × 1.07) = 140; half blocks incl. waste = ceil(14 × 1.07) = 15
jointing mass = 8.11 m² × 15 kg/m² = 121.65 kg → 5 bags
FAQ
Why do I need to enter a half-block percentage instead of the calculator working it out? The number of half/corner blocks in a real course layout depends on how the wall length divides against the block module at every corner and opening jamb — deriving it exactly would require a full per-course layout, which this calculator doesn't build. The percentage is a disclosed estimate you can adjust to match your own block's cut allowance.
What's the difference between mortar and glue jointing?
Mortar (a sand-cement bed joint, typically 8–15 mm) and thin-bed glue (a much thinner
adhesive joint, typically 1–3 mm) have very different consumption rates per m² — adjust
Jointing consumption accordingly when switching between them; the calculator doesn't set a
different default automatically.
Why doesn't the calculator cite a standard?
No standard covering ceramic hollow block or jointing quantities was found with sufficient
confidence, so meta.standards is left empty.
Assumptions and limits
Block count is area-based (net wall area ÷ single block footprint), not a real per-course running-bond layout. The half-block fraction, jointing method's consumption rate, and bag size are all disclosed estimates you can adjust.