Block Wall Calculator
With the three tonnes of blockwork nobody weighs.
Work out Block Wall. With the three tonnes of blockwork nobody weighs. Names the misconception directly.
Blocks to order
250
238 needed plus waste · 24 m² over 11 courses
Blocks per square metre comes from the block size plus one joint in each direction — a 440 × 215 block with 10 mm joints occupies 450 × 225, which gives 9.88 per square metre rather than the 10.6 the bare block size suggests. The weight figure matters more than people expect. A 10 × 2.4 m dense concrete wall is well over three tonnes, which is a real consideration for foundations, for lintels over openings, and for whether one person can build it in a day. Aircrete weighs less than half as much and insulates far better, at the cost of compressive strength and fixing reliability. Which of the three matters most is the actual decision, and the block size is downstream of it.
How the Block Wall Calculator works
Blocks, courses and mortar for a wall, with openings deducted and the finished weight. That weight matters for foundations, for lintels over openings, and for whether one person can build it in a day.
Also known as: how many blocks do i need · blocks per square metre · concrete block wall quantity · how much does a block wall weigh
Frequently asked questions
How many blocks are in a square metre?
9.88 for a UK 440 × 215 block with 10 mm joints, because the block plus joints occupies 450 × 225. The bare block size would suggest 10.6, which is why the joint has to be included.
Should I deduct openings?
For anything above about a square metre, yes. Below that the cutting waste around the opening roughly cancels the saving, so deducting a small window gains you nothing.
How much does a block wall weigh?
A 10 × 2.4 m dense concrete wall is over three tonnes. Aircrete is under half that, which is a real consideration for foundations and for lintels over openings.
What waste allowance should I use?
Five percent for a simple rectangular wall, ten for anything with openings, corners or cutting. Blocks break in transit and the last course almost always needs cutting.
Aircrete or dense concrete?
Aircrete is lighter, warmer and easy to cut, but weaker in compression and less reliable for heavy fixings. Dense blocks take load and fixings better and are much harder work to lay.
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