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How to calculate blockwork quantities.
Blockwork is measured in square metres of wall, then converted to a number of blocks. Openings are deducted and an allowance is added for breakage.
Blocks per square metre
A common block face is 400 mm long and 200 mm high, which is 0.08 m². One square metre of wall needs 1 ÷ 0.08 = 12.5 blocks with no joints. With 10 mm mortar joints the effective face is 410 mm × 210 mm = 0.0861 m², so one square metre needs about 11.6 blocks. Block thickness (commonly 100, 150 or 200 mm) does not change the count per square metre. It changes the volume of the wall and the price of each block.
Steps
- Measure the gross wall area: length × height, wall by wall and level by level.
- Deduct openings: doors, windows and large service holes.
- Multiply the net area by blocks per m².
- Add an allowance for breakage and cutting, commonly 3 to 5 percent.
- Count lintels and other special units separately, as numbers or metres.
Worked example
Wall 20 m long × 3 m high: gross area 60 m².
Openings: one door 1.0 × 2.1 = 2.10 m² and two windows 1.2 × 1.2 = 2.88 m². Total 4.98 m².
Net area: 60 − 4.98 = 55.02 m².
Blocks with 10 mm joints: 55.02 × 11.6 ≈ 639. Blocks with no joints: 55.02 × 12.5 ≈ 688.
Use the joint figure for ordering and keep the no-joint figure as an upper bound.
Related finishes
The same net wall area drives plaster and paint on both faces, so one measurement feeds several bill items. This is the idea behind take-off software: measure once, price many items.
Guides by TapeLine, quantity take-off software from Natha & Co, founded by Natha Mohamed M.M.
Try Free Beta Version See the 3D take-off
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