Autoclaved Aerated Concrete (AAC) Block Calculator
About AAC Block Calculation
The Autoclaved Aerated Concrete (AAC) block calculator determines the number of blocks required for building walls and partitions. It calculates block quantities and the number of masonry courses based on the structure dimensions, horizontal joint thickness, and window and door openings.
You can calculate a single wall or an entire house using a selected layout of internal walls. Blocks for main walls and partitions are calculated separately because their dimensions may differ.
Guidelines and recommendations
Determining masonry dimensions and area
Single wall. Masonry area is calculated by multiplying wall length by wall height. The structure dimensions are entered in metres, and the result is expressed in square metres (m²).
House walls. For a rectangular external outline, the calculated wall length is determined along the wall centre lines, taking the masonry thickness into account:
Lw = 2 × (A + B) - 4 × T
Here A and B are the external length and width of the house (m), and T is wall thickness (m). Subtracting four wall thicknesses accounts for corner connections without counting their volume twice.
Internal walls. Their calculated length depends on the selected floor plan. For sections between external walls, the internal dimensions obtained after subtracting wall thickness are used. For layouts with an offset, the relevant section length is also included. If it exceeds the available space, the value is limited and rounded down to the nearest 0.1 m.
If internal wall C is designated as load-bearing, its length is added to the main wall length. Otherwise, it is counted with the partitions. The height of internal walls is taken as equal to that of external walls.
Opening area. For each type of window and door, the area of one opening is multiplied by the number of openings. The resulting areas are added together and subtracted from the corresponding total wall area:
Sm = Lw × H - So
Here H is wall height (m), and So is the total window and door opening area (m²). Openings are deducted separately for main walls and partitions. If the opening area exceeds the corresponding wall area, the calculation is stopped until the dimensions are corrected.
Calculating the number of AAC blocks
Calculated face area of one block. To determine the block quantity, the area of the block face is used: block length multiplied by block height plus horizontal joint thickness. Block and joint dimensions entered in millimetres are first converted to metres.
Sb = l × (h + t)
Here l is block length (m), h is block height (m), and t is horizontal joint thickness (m).
Number of blocks. The net masonry area is divided by the calculated face area of one block. The result is always rounded up to a whole block:
Nb = ⌈Sm / Sb⌉
For example, with a block 600 mm long and 200 mm high and a 3 mm horizontal joint, the calculated face area is 0.6 × 0.203 = 0.1218 m². For 10 m² of masonry, 83 blocks are required after rounding up.
The quantity is determined from the total area, so individual whole and cut blocks are not laid out course by course. No additional increase factors are applied: the consumption factor is 1.00.
Number of masonry courses
Course height. The calculation includes block height plus one horizontal joint. With a 200 mm high block and a 3 mm joint, the calculated course height is 203 mm.
The number of courses is calculated from wall height, allowing for the absence of a horizontal joint above the final course:
Nr = ⌈(H + t) / (h + t)⌉
All values in the formula are expressed in metres. The result is rounded up because a partial top course also counts as a separate masonry course.
The number of courses for main walls and partitions is calculated independently if the block heights differ.
Joint thickness and block dimensions
Horizontal joints. Thin-joint AAC masonry commonly uses special adhesives with a layer thickness of about 1-3 mm. The calculator's default value is 3 mm. The actual thickness should follow the recommendations of the block and adhesive manufacturers.
Only the horizontal joint is included in the calculated block face area. Vertical joints are not added to block length. This corresponds to the simplified area-based quantity calculation used here.
AAC block dimensions. Common block lengths are 600-625 mm, with heights of 200-250 mm. Thickness depends on the intended application. Blocks 300-400 mm thick are often used for external walls, while 75-150 mm blocks are common for internal partitions. These are indicative sizes, not universal requirements.
Block thickness determines the thickness of the corresponding wall. In a house calculation, it also affects the geometric length of masonry sections. For a single wall, the block quantity is determined by its area and the dimensions of the block face.
Total quantity and European standards
Total quantity. If main walls and partitions use blocks of identical length, thickness and height, their calculated quantities are added together. If the block sizes differ, the results remain separate so the requirement for each size can be determined.
European standards. EN 771-4:2011+A1:2015, "Specification for masonry units - Part 4: Autoclaved aerated concrete masonry units", sets requirements for AAC block characteristics, including dimensions and permitted deviations.
EN 1996-2:2024, "Eurocode 6 - Design of masonry structures - Part 2: Design considerations, selection of materials and execution of masonry", provides provisions for material selection and masonry execution. The calculator's AAC block quantity calculation is based on the structure's geometric dimensions and does not apply structural strength factors.
FAQs
Why does the number of AAC blocks change when the joint thickness changes?
Horizontal joint thickness affects the calculated height of each course and the masonry area assigned to one block. Increasing the joint thickness may slightly reduce the calculated number of blocks. The effect is usually small but becomes more noticeable over a large wall area.
How are windows and doors accounted for in an AAC block calculation?
The area of each opening is determined from its width and height, multiplied by the number of identical openings. The total is then deducted from the masonry area before calculating the block quantity. Partition door openings are treated separately from windows and external doors.
Why might the calculated block quantity differ from the actual requirement?
The AAC block calculator determines quantities from the total masonry area rather than the placement of individual units. During construction, some blocks need to be cut to complete partial courses and sections around openings. Therefore, the actual number of full blocks may differ from the geometric calculation.
How are AAC blocks calculated for a house with an internal load-bearing wall?
An internal load-bearing wall is included with the main house walls when marked accordingly in the selected layout. Its calculated length is added to the total main wall length, after which the block quantity is determined from their combined area. Other internal walls are calculated as partitions.
Why does the calculator not always show a total number of blocks?
If different block sizes are used for walls and partitions, their quantities are displayed separately. This makes it possible to determine the number of units needed for each size. A combined total appears only when the block length, thickness and height are all identical.