Foam Concrete Block Quantity Calculator
About Foam Concrete Block Calculation
The foam concrete block calculator determines the number of blocks needed to build walls and partitions. It can be used to estimate materials for a single wall or a house, taking into account the floor plan, masonry dimensions, horizontal joint thickness, and window and door openings.
The calculation is based on the geometry of the structure. Different block sizes may be used for external walls and internal partitions. The results show the number of courses and blocks required.
Guidelines and recommendations
Calculating wall area
Single wall. The area is calculated by multiplying the wall length by its height. Both measurements are entered in metres.
Sw = L × H
Here Sw is wall area in m2, L is length in metres, and H is height in metres.
House walls. First, the total effective length of external walls is determined from the selected building shape. For a rectangular outline, the formula is:
Lext = 2 × (A + B) - 4 × t
Here A and B are the outside dimensions of the house in metres, and t is external wall thickness in metres. Subtracting four wall thicknesses gives the centreline length of the masonry, avoiding double-counting at the corners.
For more complex floor plans, the external outline is calculated in the same way. Depending on the selected layout, additional internal sections are included:
- Layout 1 - external walls only.
- Layout 2 - one internal wall of length B - 2t.
- Layout 3 - an internal wall of length B - 2t plus a section of length AB.
- Layout 4 - an internal wall of length B - 2t plus a section of length A - 2t.
- Layout 5 - an internal wall of length B - 2t plus two sections of length AB.
- Layout 6 - two internal walls, each of length B - 2t.
Negative calculated lengths are treated as zero. If internal wall C is designated as load-bearing, its length is added to the group calculated using the main wall blocks. The remaining internal sections are treated as partitions.
For layouts with offset AB, the permitted offset is limited by the building dimensions and the thickness of adjoining walls. If the entered value exceeds the limit, it is reduced to the next lower increment of 0.1 m.
Masonry area. The total effective length of each wall group is multiplied by its height:
Swalls = Lwalls × H
The height of internal partitions is taken to be the same as that of the main walls. Wall and partition areas are calculated separately because the block dimensions may differ.
Allowing for window and door openings
Opening area. For each window or door size, the width is multiplied by the height and the number of identical openings. Dimensions are converted from millimetres to metres.
Sopen = Σ (b × h × n)
Here b is opening width in metres, h is height in metres, and n is the number of openings of that size. The symbol Σ denotes the sum of all opening areas.
The resulting area is subtracted from the total area of the relevant walls:
Smasonry = Swalls - Sopen
Windows and external doors are deducted from the main walls, while doors in internal partitions are deducted from partition area. If the combined opening area exceeds the corresponding wall area, the block calculation stops until the dimensions are corrected.
Masonry joint thickness
Horizontal joint. The mortar or adhesive thickness between courses is included when calculating the block quantity. It increases the effective height of each block, but not its length.
The following values are commonly used for foam concrete block masonry:
- 2-5 mm - thin-bed adhesive for accurately dimensioned blocks.
- 8-12 mm - conventional masonry mortar, also used where block dimensions are less precise.
These are typical ranges. The actual joint thickness should follow the recommendations of the block and masonry-mix manufacturers. The calculator's default is 3 mm.
Effective block dimension. The horizontal joint thickness is added to the block height:
heff = hblock + s
Here hblock is block height and s is joint thickness, both in millimetres. Vertical joints are not included in the effective block dimension.
Number of courses and blocks
Number of courses. This is calculated from the wall height and the combined height of a block and a horizontal joint. The calculation allows for N - 1 horizontal joints between N courses.
Ncourses = ⌈(H + s) / (h + s)⌉
Here H is wall height, h is block height, and s is horizontal joint thickness. All dimensions must use the same unit. The symbols ⌈ ⌉ indicate rounding up to the nearest whole number.
For example, a wall 2700 mm high built with 200 mm blocks and 3 mm joints requires 14 courses. The top course can be cut to the required height.
Number of blocks. The calculation uses the net masonry area after subtracting openings. This is divided by the effective face area of one block, including its horizontal joint:
Nblocks = ⌈Smasonry / (l × (h + s))⌉
Here Smasonry is masonry area in m2, l is block length, h is block height, and s is horizontal joint thickness. Block and joint dimensions are first converted to metres.
For example, for 10 m2 of masonry using blocks 600 mm long and 200 mm high with 3 mm joints, the result is:
Nblocks = ⌈10 / (0.6 × 0.203)⌉ = 83
The quantity is calculated from the total area, rather than rounding the number of blocks in each course separately. Fractions are rounded up to a whole block. No additional percentage factors are applied to the result.
Total quantity. Walls and partitions are calculated separately. If their blocks have exactly the same length, width and height, the quantities are added together:
Ntotal = Nwalls + Npartitions
When the block sizes differ, the results remain separate so that each block size has its own quantity.
European standards
The following European standards are relevant when selecting masonry materials and construction methods:
- EN 1996-2 - Eurocode 6. Design of masonry structures. Part 2. Design considerations, selection of materials and execution of masonry.
- EN 998-2 - Specification for mortar for masonry. Part 2. Masonry mortar.
These standards set general requirements for materials and masonry execution. The geometric calculation of foam concrete block quantities uses the dimensions of the structure and blocks, not standardised material-consumption factors.
FAQs
Why does a thicker joint reduce the calculated number of foam concrete blocks?
A thicker horizontal joint increases the height of masonry represented by each block. Slightly fewer blocks are therefore needed for the same wall area. The difference is usually small but becomes more noticeable for large masonry areas and shorter blocks.
Why can an area-based block estimate differ from counting each course?
The calculator estimates block quantities from the total masonry area, including horizontal joints. This method allows for the use of cut block pieces and rounds the result only after the entire area has been calculated. Counting and rounding each course separately may produce a different total.
How are internal load-bearing walls included?
When internal wall C is designated as load-bearing, it uses the same block dimensions as the main walls. Its length is added to that wall group rather than to the partitions. This ensures the quantities are assigned to the appropriate block sizes.
How do foam concrete block dimensions affect the result?
Longer blocks reduce the number needed to cover the same masonry area. Taller blocks also reduce the number of courses. Block width determines wall thickness and affects house geometry, but does not enter directly into the area-based block quantity formula.
Why is a combined block quantity not always displayed for a house?
If external walls and partitions use different block sizes, the calculator displays each quantity separately. A combined total appears only when block length, width and height all match. This avoids mixing different products into a single result.