Masonry
Quick answer: For 10 m² of wall built with 25 × 19 cm blocks and 1 cm joints you need about 202 blocks including 5% extra.
Calculate blocks and bonding material for masonry
How the calculation works
Enter the wall dimensions or area, openings, block type, joint width and reserve. The calculator subtracts openings, works out blocks per m² and adds the reserve.
Formula and assumptions
Blocks per m² = 1 ÷ ((length + joint) × (height + joint)), in metres. Blocks = effective area × blocks per m² × (1 + reserve), rounded up. Effective area = wall area − openings. The binder quantity uses the product norm (L/m², kg/m², kg/m³ or m² per pack) or a geometric estimate of the joint volume, with separate reserves for blocks and binder.
Worked example
Wall 10 m² with no openings, block 25 × 19 cm, 1 cm joint: 1 ÷ (0.26 × 0.20) = 19.23 blocks/m². 10 × 19.23 = 192.3; with 5 % reserve → 201.9 → 202 blocks.
More worked examples
- Wall 24 m² with 4 m² of openings → 20 m² net, block 25 × 19 cm, joint 1 cm, reserve 5 %: 20 × 19.23 = 384.6; with reserve 403.8 → 404 blocks.
- Wall 8 × 2.5 m = 20 m², no openings, block 30 × 20 cm, joint 1 cm: 1 ÷ (0.31 × 0.21) = 15.36 blocks/m². 20 × 15.36 = 307.2; with a 5 % reserve 322.6 → 323 blocks.
Blocks 25 × 19 cm, joint 1 cm (19.23 blocks/m²)
| Wall area (m²) | Blocks (no reserve) | Blocks with 5 % reserve |
|---|---|---|
| 10 | 193 | 202 |
| 20 | 385 | 404 |
| 30 | 577 | 606 |
| 50 | 962 | 1010 |
| 100 | 1924 | 2020 |
What affects real consumption
- Real joint width and bonding pattern (head joints).
- Breakage and cutting at openings and corners.
- Deviation of block dimensions from nominal.
Common mistakes
- Not subtracting doors and windows from the wall area.
- Ignoring the joint thickness, which changes the number of blocks per m².
- Buying without a reserve for breakage and cutting.
Frequently asked questions
Should I add a reserve for blocks?
A few percent is usual for breakage and cutting; you set the reserve value yourself.
Is wall thickness taken into account?
Thickness is part of the chosen block: it sets the wall volume and per-m³ binder norms, while blocks per m² depend on length, height and joint.
How many blocks per m² for a 25 × 19 cm block?
With a 1 cm joint it is 1 ÷ (0.26 × 0.20) = 19.23 blocks per m², so roughly 20 blocks.
How many blocks for a 50 m² wall?
Without openings and with a 5 % reserve you need about 1010 blocks of 25 × 19 cm with a 1 cm joint.
Can the calculator work out site-mixed mortar and how much wall I can build with the material I have?
Yes. For cement, lime and sand you enter the ratio, yield and bulk densities (there is no universal factor) and get cement and lime in bags and sand in m³. The reverse calculation from a number of blocks and an amount of binder shows the possible wall area and the limiting material.
Can I calculate a gable wall, a circular wall or an arch and see how many blocks are cut?
Yes. Besides rectangular walls, house gables, triangular gables and trapezoids are supported, and the 2D layout colours bricks red and aerated concrete off-white and shows joints plus whole and cut pieces. Circular walls (up to 360°) and semicircular or segmental arches are calculated geometrically, with wedge joints or cut wedges; the result says nothing about load capacity.
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Publisher: Art-Visum d.o.o. · Content reviewed:
Calculations use common consumption rates and manufacturers' technical data sheets; results are estimates. Methodology · Standards · About