Block Brick Calculator
Estimate exactly how many concrete blocks, bricks, bags of cement and cubic metres of building sand your wall needs before you order. Many South African walls combine both, blockwork below damp-proof course or for a retaining base, brickwork above, so this tool lets you cost either material, or switch between them, in one place. Pick a common project or enter your own wall dimensions to get an instant materials breakdown with wastage included.
Calculate My Materials ↓Block & Brick Calculator
Select a project type or build a custom wall, choose concrete block, standard brick, or maxi brick, then press Calculate to see your full materials list.
Total Units Needed
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Project summary
Full materials breakdown
| Material | Quantity | Unit | Notes |
|---|
This total is based on the coverage rate for your chosen block or brick type across your wall area.
Concrete blocks (390 x 190mm face) work out to roughly 12.5 blocks per square metre no matter the block thickness, while a single-skin (110mm) wall built with standard South African bricks needs roughly 50 bricks per square metre, and a double-skin (220mm) wall needs roughly 100 bricks per square metre. For every 1000 bricks or blocks laid with a standard Class II mortar mix, plan for around 3 bags of cement and 0.6 cubic metres of building sand, plus 5-10% extra for wastage. Use the calculator above for an exact total based on your specific wall.
How to Use the Block Brick Calculator
Four quick steps to an accurate block, brick and mortar estimate for your wall.
- 1 Choose your project. Pick a common preset such as a blockwork boundary wall or brick garage wall, or select “Custom Wall” to enter your own length, height and any openings to deduct.
- 2 Select block or brick type. Choose Concrete Block, Standard/Stock brick, or Maxi brick depending on what you are building with.
- 3 Set your wall type and wastage. Choose single skin or double skin, and leave the wastage allowance ticked to add a standard 10% buffer for breakage and cutting.
- 4 Press Calculate. Your total blocks or bricks, cement bags and sand volume will appear instantly. Use “Copy Result” to save it for your project budget.
The Block, Brick & Mortar Formula
Block and brick quantities in South Africa are based on a fixed coverage rate per square metre for each unit type, so the calculation is a straightforward multiplication.
If Wastage Applied: Units Needed = Units Needed × 1.10
Cement (50kg bags) = Units Needed × 0.003 (3 bags per 1000 units)
Building Sand = Units Needed × 0.0006 m³ (0.6m³ per 1000 units)
Wall area is multiplied by the coverage rate for the chosen block or brick size and wall thickness to get the raw unit count, which is then rounded up to a whole unit. Cement and sand quantities follow the same per-1000-unit ratio used for a standard Class II mortar mix, then rounded up to the nearest full bag and the nearest 0.1 cubic metre of sand for practical ordering.
Worked Examples
Real project calculations using standard South African coverage rates, so you can see exactly how each total is built.
Example 1: Blockwork boundary wall, concrete block, single skin, with wastage
| Wall area (10m x 1.8m) | 18 m² |
| Blocks needed (18 × 12.5, +10% wastage) | 248 blocks |
| Cement (248 × 0.003, rounded up) | 1 bag |
| Building sand (248 × 0.0006) | 0.2 m³ |
Example 2: Brick garage wall, maxi brick, double skin, no wastage
| Wall area (6m x 2.4m) | 14.4 m² |
| Bricks needed (14.4 × 56, rounded up) | 807 bricks |
| Cement (807 × 0.003, rounded up) | 3 bags |
| Building sand (807 × 0.0006) | 0.5 m³ |
Example 3: Brick room addition, standard brick, single skin, with wastage
| Wall area (10m x 1.8m) | 18 m² |
| Bricks needed (18 × 50, +10% wastage) | 990 bricks |
| Cement (990 × 0.003, rounded up) | 3 bags |
| Building sand (990 × 0.0006) | 0.6 m³ |
Block Brick Calculator: The Complete Guide
Getting block, brick and mortar quantities right before you order saves you unnecessary trips to the builders merchant, avoids costly under-ordering delays, and stops you from overspending on materials you will never use. This guide explains the difference between concrete blocks and clay bricks, how South African coverage rates work, and how much mortar you actually need for either material.
Block or brick, which should you use?
Concrete blocks and clay bricks solve slightly different problems, and many South African walls actually use both. Blocks are larger, so far fewer units are needed to cover the same wall area, which speeds up construction and reduces labour and mortar costs. This makes them a common choice for boundary walls, retaining walls, foundation stem walls below damp-proof course, and commercial or industrial structures. Clay bricks, whether standard/stock or maxi, are more widely used above ground for house walls, internal partitions and face-brick finishes, where the smaller unit size gives finer detailing around openings and corners. It is common practice on a single project to build the plinth or retaining section in blockwork and the walls above in brick, so this calculator lets you switch between block and brick types for each section of the job.
How are block and brick quantities calculated?
Coverage in South Africa is based on a fixed number of units per square metre of wall, determined by the unit’s face size and a standard 10mm mortar joint. Multiply your wall area by the coverage rate for your chosen block or brick type and wall thickness to get the number of units required, then add cement and sand for the mortar that binds them together.
Standard block and brick sizes in South Africa
- Concrete block: 390mm face length x 190mm face height, available in several thicknesses (commonly 90mm, 140mm and 190mm) to suit different wall depths. Popular for boundary walls, retaining walls, and commercial or industrial structures, since a block wall goes up with far fewer units than the equivalent brick wall.
- Standard/Stock brick: 222mm x 106mm x 73mm. The most widely used brick for house walls, both for plastered stock brick finishes and unplastered face brick walls of the same size.
- Maxi brick: 290mm x 140mm x 90mm. A larger clay or concrete brick that needs fewer units per square metre than a standard brick and speeds up construction, commonly used for structural and load-bearing walls.
- Paving brick: Sized and laid differently to wall blocks and bricks, since they are set flat rather than stacked in courses. Use a dedicated paving calculator rather than this wall-based tool.
Half-brick vs full-brick (single skin vs double skin) walls
A single-skin, or half-brick, wall is one unit thick and typically measures 110mm for standard bricks. This is the standard thickness for internal walls, garden walls and many boundary walls. A double-skin, or full-brick, wall is built as two layers and measures roughly 220mm thick, and is used for external loadbearing walls that need to carry the weight of a roof or upper floor. Double-skin walls use roughly twice as many bricks per square metre as single-skin walls of the same brick type. Concrete blocks are available directly in a range of thicknesses instead, so the coverage rate per square metre stays the same regardless of which block width you choose.
How much cement and sand do you need for mortar?
The Clay Brick Association of Southern Africa’s guidance for a normal, Class II strength mortar (a cement-rich mix suitable for most loadbearing and freestanding walls) works out to roughly 3 bags of 50kg cement and 0.6 cubic metres of building sand for every 1000 bricks laid, or about 1 bag of cement to every 3 wheelbarrows of sand. This calculator applies that same per-1000-unit ratio to concrete blocks as an estimate, since exact block mortar consumption depends on joint size and block type, so always confirm final quantities with your supplier for large or structural block projects. For plaster work, a rough guide is about 10 bags of cement and 2 cubic metres of sand per 100 square metres at 15mm thickness.
Mortar mix ratios explained
Most residential brickwork and blockwork in South Africa uses a 1:6 cement-to-sand mortar mix by volume, which produces a Class II mortar suitable for freestanding walls, garden walls, parapets and general loadbearing masonry. For structures exposed to severe dampness or requiring extra strength, such as certain retaining walls or below damp-proof-course work, a stronger 1:4 mix is often specified instead. Always check the mix ratio required for your specific structure, especially for retaining walls or anything load-bearing, ideally with a structural engineer or your local building inspector.
Why wastage allowance matters
Even careful bricklaying and blocklaying produce breakages, off-cuts around openings, and losses during delivery and handling. Adding 5-10% extra to your calculated block or brick count is standard practice in South African construction and helps avoid a second, smaller and often more expensive top-up order partway through a project.
Tips for reducing waste and overspending
- Measure openings carefully. Deduct the area of doors and windows from your total wall area rather than ignoring them, especially on smaller walls where openings make up a larger share of the surface.
- Buy from the same batch. Face bricks in particular can vary slightly in colour between production batches, so order your full quantity, plus wastage, from one batch where possible.
- Store blocks and bricks off the ground. Stacking on pallets or boards away from mud and standing water reduces breakage and staining before they are used.
- Confirm supplier stock before ordering. Popular block and brick sizes can be on backorder in some regions, so confirm availability before finalising your building schedule.
- Get a second opinion for structural or retaining walls. This calculator is for general material estimation only and does not replace an engineer’s design for retaining walls or loadbearing structures.
Methodology
Coverage rates used in this calculator reflect widely published South African construction industry figures for standard 10mm mortar joints: 12.5 concrete blocks per square metre based on a 390mm x 190mm block face, 50 standard bricks per square metre for a single-skin (110mm) wall, and 28 maxi bricks per square metre for a single-skin wall. Double-skin brick figures are calculated as double the single-skin rate; block coverage stays the same regardless of block thickness. Cement and sand quantities are based on the Clay Brick Association of Southern Africa’s published guidance of roughly 3 bags of cement and 0.6 cubic metres of sand per 1000 bricks for a Class II mortar mix. Actual requirements can vary based on unit batch size, mortar joint thickness, wall bonding pattern, and site conditions, so always confirm exact quantities with your supplier or builder before ordering for a project where accuracy is critical.
Assumptions used in this calculator
- All coverage rates assume a standard 10mm mortar joint.
- Wastage, when applied, adds an estimated 10% to the raw block or brick count.
- Cement and sand figures use the same per-1000-unit ratio for bricks and concrete blocks as a general estimate.
- Preset projects use approximate typical dimensions and may not reflect your exact wall size or bonding pattern.
- This tool does not calculate reinforcing steel, foundations, plaster, or paint quantities.
Frequently Asked Questions
A standard South African concrete block, with a 390mm x 190mm face and a 10mm mortar joint, works out to roughly 12.5 blocks per square metre of wall, regardless of the block’s thickness (commonly 90mm, 140mm or 190mm). Use the calculator above for an exact figure based on your wall size.
For a standard South African brick (222 x 106 x 73mm) with a 10mm mortar joint, you need approximately 50 bricks per square metre for a single-skin (110mm) wall, and roughly 100 bricks per square metre for a double-skin (220mm) wall. Maxi bricks need fewer units, at around 28 per square metre single skin.
It depends on the structure. Blocks are commonly used for boundary walls, retaining walls, and sections below damp-proof course, since fewer, larger units mean faster building and less mortar. Clay bricks, whether standard or maxi, are more commonly used above ground for house walls, internal partitions and face-brick finishes. It’s common to combine both on one project, block below, brick above, which is why this calculator lets you switch between unit types.
A half-brick wall, also called single skin, is one brick thick, typically around 110mm, and is commonly used for internal walls and garden or boundary walls. A full-brick wall, or double skin, is built with two layers of brick for a thickness of around 220mm, and is used for external loadbearing walls that need to support a roof or upper floor.
For a standard Class II mortar mix, the Clay Brick Association of Southern Africa’s guidance works out to roughly 3 bags of 50kg cement and 0.6 cubic metres of building sand per 1000 bricks, or about 1 bag of cement to every 3 wheelbarrows of sand. This calculator applies the same ratio as an estimate for concrete blocks. Stronger mixes for loadbearing or exposed structures use more cement relative to sand.
A wastage allowance of 5-10% is standard practice in South African construction to cover breakage, cutting around openings, and losses during delivery and handling. This calculator applies an estimated 10% when the wastage option is selected.
Yes. Alongside concrete block, you can select standard/stock brick or maxi brick from the dropdown, and the calculator will apply the correct coverage rate and mortar estimate for each unit type and wall thickness.
This calculator provides a general materials estimate only. For retaining walls, loadbearing structures, or anything requiring council approval, it’s best to consult a structural engineer or your local municipality’s building control department before starting construction.