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Quick answer
A 390 × 190 mm block face with 10 mm joints covers 0.08 m², or 12.5 blocks/m². For a net 21 m² wall, one leaf and 10% waste require 289 blocks.
How it works
Use this block brick calculator for South Africa to estimate masonry units from measured walls and openings. Compare actual unit coverage and full-pack quantities.
Formula
Blocks = net wall area × units per m² × leaves × (1 + waste ÷ 100), rounded up.
Assumptions and common mistakes
Check units, input values and the method before relying on an estimate. Review the existing tool notes and official sources below.
Formula
Blocks = net wall area × units per m² × leaves × (1 + waste ÷ 100), rounded up.
How to use the block brick calculator
Start with the block example or select a brick size. The initial 390 mm length and 190 mm height are the face dimensions; width is not multiplied into the wall-face coverage. Add measured sections and openings, then enter leaves, allowance and pack size.
Block brick calculator per m²
Add the joint once to each repeating face dimension. For the example, 400 mm × 200 mm gives 80,000 mm². Dividing one million by that area gives 12.5 blocks per square metre. Waste and pack rounding are separate steps.
Comparing different block widths
Blocks with the same face dimensions can have equal units per square metre while having different widths, strengths or uses. Equal quantities do not make the units interchangeable. Use the width and strength specified for your wall.
Hollow units and mortar
Do not subtract hollow cores from the block count. Voids and shell bedding affect mortar consumption instead. The mortar calculator takes a user-confirmed rate because a single percentage reduction cannot describe every hollow block.
Brick versus block estimates
Compare the full job, including mortar, cutting, reinforcement, delivery and labour. A lower unit count or cheaper piece price does not by itself establish the cheaper suitable wall. Different leaves should be calculated separately when their products differ.
Brick and block coverage comparison
| One leaf, no waste | Face L × H (mm) | Joint (mm) | Units per m² |
|---|---|---|---|
| Stock/face example | 222 × 73 | 10 | 51.932 |
| Same face, larger joint | 222 × 73 | 12 | 50.277 |
| Maxi example | 290 × 90 | 10 | 33.333 |
| Flat-maxi example | 288 × 88 | 10 | 34.242 |
| Block example | 390 × 190 | 10 | 12.5 |
Geometric examples for one leaf, without waste. These are not universal product specifications.
Last reviewed: 15 October 2026. Reviewed by the 99tools team. Editorial and corrections policy.
Quantity estimates only. Product suitability, wall stability and any structural design must be confirmed for the job.
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- How Many Bricks per Square Metre?
- What Does a Brick Calculator Need for Accuracy?
- Compare Brick Calculators: Cashbuild, Build it and BUCO
- How Much Does It Cost to Build a Brick Wall in South Africa?
- Maxi Bricks vs Stock Bricks: Quantity and Size
- How to Calculate Paving Bricks for a Driveway or Patio
- Interlocking Pavers: Coverage, Pallets and Supplier Checks
- Brick Mortar for Maxi Bricks and Thin Brick: What to Enter
- Single vs Double-Skin Brick Walls: Quantity Guide
- What Is Brickforce? Uses, Sizes and Roll Length
- Brickforce Prices: Compare Roll Quotes in South Africa
- Sand and Cement Mix Ratios: Mortar, Plaster and Screed
- How Much Sand and Cement per m² or 1,000 Bricks?
- Maxi Brick Prices and Pallets: How to Compare Quotes
- How to Measure Wall Plaster Area in m²
- Cement, Gypsum, Lime and Pool Plaster Quantities
Frequently asked questions
How many 390 × 190 mm blocks do I need per m²?
With 10 mm bed and vertical joints, the geometric coverage is 12.5 blocks/m² for one leaf, before waste.
Does block width change blocks per m²?
Width does not change face coverage when length and height stay the same. It still matters for wall design and product suitability.
Should I deduct the holes in hollow blocks?
No. Each installed block is counted as one unit. Its voids affect mortar and other materials, not the wall-face unit count.
Related calculators
Brick Calculator South Africa
Use this brick calculator for South Africa to estimate stock or face bricks from wall sizes, openings, mortar joints and waste. Add unequal wall sections.
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Estimate brick mortar, cement and sand, premix bags or thin brick product bags. Enter confirmed rates for stock or maxi bricks in South Africa.
Brick Wall Calculator South Africa
Calculate single or double-skin wall bricks and costs using your quotes. Check maxi or cement brick coverage and download results as an Excel-ready CSV.
Brickforce Calculator South Africa
Calculate brickforce metres, full rolls and quoted cost. Enter specified layers, roll length and lap allowances, then compare the same product and size.
Helpful guides
How Many Bricks per Square Metre?
Bricks per m² depend on the actual wall-face dimensions, mortar joints and number of leaves. A 222 × 73 mm face with 10 mm joints gives about 51.932.
Foundation Quantities: Strip, Pad and Raft
Measure foundation concrete using the specified geometry. Strips, pads and rafts need different take-offs, but a quantity calculator cannot select a safe.