Concrete and Cinder Block Calculator
About Concrete and Cinder Block Calculation
The Concrete and Cinder Block Calculator estimates the number of concrete, cinder and other rectangular masonry blocks needed for a single wall or the walls of a house, garage or other building with internal partitions. It also supports ceramic, expanded-clay concrete and sand-concrete blocks. The calculation accounts for structural dimensions, horizontal bed joints, internal wall layout and the areas of window and door openings.
Guidelines and recommendations
Determining masonry dimensions
Masonry length. For a single wall, the specified length in metres is used. For a rectangular building, the external perimeter is calculated from length A and width B. Four wall thicknesses are then deducted to avoid counting the blocks at the building corners twice.
Lwalls = 2 × (A + B) − 4 × t
Here, A and B are the external building dimensions in metres, while t is the wall thickness in metres, corresponding to the width of the selected block. For example, a 10 × 10 m building with 0.5 m thick walls has a calculated masonry length of 38 m rather than the 40 m external perimeter.
Internal walls. Their lengths are derived from the selected building layout. If internal wall C is load-bearing, its length between the external walls is added to the masonry length calculated for the main blocks. The other internal sections are calculated as partitions with their own block dimensions. For layouts with an offset, the specified AB distance is used. If it exceeds the available length, the value is capped and rounded down to 0.1 m.
Masonry area. The calculated length of each wall type is multiplied by the common wall height in metres. This produces the area in m2 used to calculate the number of blocks. Internal partitions are assumed to have the same height as the other walls.
Accounting 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. The dimensions are converted from millimetres to metres before the areas are added together.
Sopenings = Σ (width × height × quantity)
The resulting area is subtracted from the area of the corresponding masonry. Windows and doors are included for the main walls, while internal door openings are included for partitions. Deductions are made only when the relevant option is enabled. If the total opening area exceeds the masonry area, the calculator displays a warning instead of results.
Joint thickness and number of courses
Horizontal bed joint. Its thickness is added to the block height when calculating the number of courses and blocks. The default is 3 mm. Vertical joints are excluded from the calculation: their assumed thickness is 0 mm.
Number of courses. This is found from the wall height and the height of one block plus a horizontal joint. One joint thickness is also added to the wall height in the numerator, so that no additional joint is counted above the final course.
Ncourses = ⌈(H + s) / (h + s)⌉
Here, H is the wall height, h is the block height, and s is the horizontal joint thickness. All values must use the same units. The result is rounded up to a whole number. Where main walls and partitions use blocks of different heights, their numbers of courses are calculated separately.
Calculating the number of blocks
Effective face area of a block. Material quantities are calculated using the block length multiplied by its height plus the horizontal joint. The block width determines the wall thickness and affects the geometry of wall intersections, but does not directly enter the face-area calculation.
Sblock = l × (h + s)
Number of blocks. The opening area is subtracted from the masonry area. The remaining area is divided by the effective face area of one block. The resulting quantity is always rounded up to a whole number of blocks.
Nblocks = ⌈Snet / Sblock⌉
For example, a wall 6 m long and 3 m high has a masonry area of 18 m2. With blocks 600 mm long and 200 mm high and a 3 mm horizontal joint, the effective face area per block is 0.1218 m2. Without openings, the result is 148 blocks and 15 courses.
Rounding method. The numbers of courses and blocks are calculated independently. Block quantities are estimated from the overall area, without simulating the position of each block in a course, bond patterns or reuse of cut pieces. The automatic waste allowance is 0%: the additional quantity factor is 1.00.
Total quantity. Blocks for main walls and partitions are counted separately. If the length, width and height of both block types match exactly, their quantities are also added together. If the block dimensions differ, the results remain separate.
Regulatory references
Masonry joint thickness. European standard EN 1996-1-1, “Eurocode 6: Design of masonry structures — General rules”, gives joint thickness ranges of 6–15 mm for general-purpose mortar and 0.5–3 mm for thin-layer mortar. The actual thickness depends on the block type, its dimensional accuracy and the manufacturer's recommendations.
Block characteristics. European standard EN 771-1, “Specification for masonry units — Clay masonry units”, applies to clay blocks. EN 771-3, “Specification for masonry units — Aggregate concrete masonry units (Dense and lightweight aggregates)”, applies, among others, to concrete and expanded-clay concrete blocks. These standards specify product characteristics but do not prescribe an additional factor for the calculated number of blocks.
FAQs
Why doesn't the number of blocks always equal the number of courses multiplied by the blocks per course?
The calculator estimates block quantities from the masonry area but determines the number of courses from the wall height. Both results are rounded independently. Therefore, multiplying the number of courses by the number of whole blocks along the wall may give a different result from the calculated quantity.
How does joint thickness affect the number of building blocks?
A thicker horizontal joint increases the height of each masonry course. For the same wall height, this can reduce the calculated number of courses and blocks. For an accurate estimate, enter the actual joint thickness required by the chosen masonry method.
How are external wall corners and an internal load-bearing wall accounted for?
Four wall thicknesses are deducted from the external perimeter so that the corner sections are not counted twice. If internal wall C is designated load-bearing, its length between the external walls is included in the main block calculation. Otherwise, that section is calculated as a partition.
How are windows and doors of different sizes included?
The area of each type of opening is calculated from its width, height and quantity. The areas are added together and deducted from the masonry area before the number of blocks is calculated. Two different window sizes can be included, while door openings in main walls and partitions are handled separately.
What allowance for building blocks should be made when ordering?
The calculator gives the number of blocks without an extra allowance, using a factor of 1.00. Actual requirements may increase due to cutting, transport damage and the masonry bond pattern. Any additional quantity to order should be based on the laying plan and site conditions.