Concrete block calculator
Blocks are counted the same way as bricks, from the module of block plus joint.
%
Blocks needed
258
- Blocks per square metre
- 9.88
- Net wall area
- 24.80
- Courses
- 10
- Mortar volume
- 0.298
- Sand
- 595
- Approximate block weight Taking 20 kg per dense block.
- 5160
Show the working
- Wall length = 12
- Wall height = 2.4
- Block length = 440
- Block height = 215
- Mortar joint = 10
- Area of openings = 4
- Waste allowance = 5
- gross_area = 12 * 2.4 = 28.8
- Net wall area = max(28.8 - 4, 0) = 24.8
- block_area = (440 + 10)/1000 * (215 + 10)/1000 = 0.101 25
- Blocks per square metre = 0.101 25 > 0 ? 1 / 0.101 25 : 0 = 9.876 54
- Blocks needed = ceil(24.8 * 9.876 54 * (1 + 5/100)) = 258
- Courses = floor(2.4 * 1000 / (215 + 10)) = 10
- Mortar volume = 24.8 * 0.012 = 0.2976
- Sand = 0.2976 * 1.25 * 1600 = 595.2
- Approximate block weight = 258 * 20 = 5160
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- blocks per square metre = 1 / ((length + joint) x (height + joint))
A 440 by 215 mm block with a 10 mm joint gives 9.88 blocks per square metre — the familiar "ten blocks a metre".