Concrete block calculator
Estimate blocks from wall dimensions, openings, block size, joints, breakage allowance and packaging.
Concrete block calculation
Describe the wall, openings and block size: blocks, pallets and mortar bags are recalculated automatically.
Doors and windows
Each opening is deducted from the wall area.
Supply
Indicative quantities
Theoretical requirement
Added allowance
Estimated mortar
Mortar bags
Calculation details
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How does this tool work?
The concrete block calculator estimates how many blocks to order for a wall. It deducts doors and windows, accounts for the mortar joint, adds a breakage allowance and can convert the result into pallets and bags of mortar.
The gross wall area is length × height. Each door or window you add is deducted as width × height × quantity to give the net area.
The engine then uses the block module, meaning the block’s face plus one joint in each direction. With a 50 × 20 cm block and a 10 mm joint, each block occupies 0.51 × 0.21 m = 0.1071 m², so about 9.3 blocks per square metre.
The theoretical requirement is rounded up to a whole block, then the breakage allowance is added, also rounded up. This keeps a visible distinction between the geometric need and the spare blocks.
Pallets are rounded up to whole pallets. Mortar is estimated on the net area with the consumption in kg/m² you enter, then converted into bags of the chosen weight.
Block quantity should use the net wall area and the real block-plus-joint module. Doors and windows reduce the area, while cuts, corners and special blocks need to be accounted for separately.
How to use this tool
Measure the wall
Enter its length and height.
Add the openings
Deduct doors and windows with their quantity.
Choose the block
Use a common size or your own dimensions, and the planned joint thickness.
Set the supply
Enter blocks per pallet, mortar consumption and the size of the bags sold.
Concrete block formulas
The calculation uses the net wall area and the real module taken up by one block with its joint.
Gross area
A = length × height
Total wall area before openings.
Net area
net A = gross A − openings
Doors and windows are deducted.
Block count
N = net A / ((block L + joint) × (block H + joint))
The breakage allowance is then added and the result rounded up.
This tool estimates material quantities. It does not size foundations, lintels, ring beams or reinforcement; follow the project specification and applicable professional rules for those structural elements.
Use cases
Boundary or garden wall
Quickly estimate the blocks for a plain rectangular wall.
Wall with openings
Deduct a door, windows or several identical openings.
Preparing an order
Turn the number of blocks into pallets and the mortar into bags.
Examples
Plain 10 × 2 m wall
The block-plus-joint module is 0.51 × 0.21 m = 0.1071 m². 20 ÷ 0.1071 = 186.74 blocks, rounded up to 187, plus 10 spare blocks (5% rounded up).
Input
Wall 10 m × 2 m · 50 × 20 cm block · 10 mm joint · 5% allowance · 60 blocks per pallet · mortar 20 kg/m² · 25 kg bagsResult
186.74 blocks in theory; 197 blocks to order; 4 pallets; mortar 400 kg (16 bags)Same wall with a door
The door removes 1.84 m². 169.6 blocks become 170, plus 9 spare blocks, giving 179; 179 ÷ 60 gives 3 pallets.
Input
Same settings · door 0.90 × 2.04 mResult
Net area 18.16 m²; 169.6 blocks in theory; 179 blocks to order; 3 pallets; mortar 363.28 kg (15 bags)Tips and best practices
- Keep a few extra blocks for breakage and cuts, especially at corners and around openings.
- The number of blocks per pallet varies with the size and the supplier: replace the suggested value with that of your product.
- Mortar consumption depends on the block type, the joints and the laying method: use your manufacturer’s figure when it is available.
Sources and references
Frequently asked questions
How many concrete blocks are needed per m²?
It depends on the block size and the joint. A 50 × 20 cm block gives 10 blocks per m² without joints; with a 10 mm joint the 51 × 21 cm module brings this down to about 9.3 blocks per m², before the breakage allowance.
Should windows and doors be deducted?
Yes, for a more accurate estimate. You can add as many openings as you need, each with its quantity.
What breakage allowance should I plan for?
5% is a common starting point for a simple wall. Increase it when there are many cuts or the job is complex.
Does the calculator size the foundations?
No. It only calculates quantities of blocks and mortar. Foundations, lintels and reinforcement require their own design.
How are pallets calculated?
The number of blocks to order is divided by the number of blocks per pallet and rounded up to the next whole pallet: 197 blocks at 60 per pallet need 4 pallets.
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