Concrete Block Calculator
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Metric (m)
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Walls
Standard 10mm joint - approx 0.012 m² mortar per m²
Typical allowance: 5% standard work, 10% complex shapes or many cuts
Standard rate is 2.9 ties/m² (900 x 450mm pattern). Supplied in boxes of 250.
Job Costing
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UK Market Prices
Fills in the material cost fields using current UK retail prices sourced from major trade suppliers. Prices are updated regularly by BuildersCalc and give you a realistic starting point for your estimate. Always cross-check against your own quotes before finalising.
Results
| Wall | Area (m²) | Net Blocks | Waste | Total |
|---|
Total Net Blocks
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Before waste allowance
Total Waste
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Total to Order
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Rounded up to nearest 10
Mortar Required
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m² across all walls
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Frequently Asked Questions
How many concrete blocks do I need per square metre?
For a standard UK concrete block (440 x 215 mm face) with a 10 mm mortar joint, you need approximately 10 blocks per m². For a 140 mm high block (440 x 140 mm), approximately 12.5 blocks per m². Always add a waste allowance of 5-10% on top.
What is the standard UK concrete block size?
The standard UK concrete block size is 440 x 215 x 100 mm (length x height x width), giving a co-ordinating size of 450 x 225 mm with a 10 mm mortar joint. Other common sizes include 440 x 215 x 140 mm and 440 x 215 x 215 mm for loadbearing applications, as defined in BS EN 771-3.
What is the difference between dense and lightweight concrete blocks?
Dense blocks (aggregate blocks) weigh around 20 kg each, offer high compressive strength and are used for loadbearing walls and below-ground work. Lightweight aerated blocks (Thermalite, Celcon etc.) weigh 8-12 kg, cut easily and have excellent thermal performance - widely used in cavity wall inner leaves to meet Part L of the Building Regulations.
What waste allowance should I use for concrete blockwork?
Use 5% waste for simple straight walls with few cuts, 10% for typical projects with openings and corners, and 15% for complex shapes. Blocks are heavy and breakage during delivery is common - always order a small surplus as batches can vary.
What Building Regulations apply to concrete block walls?
Block walls must comply with Part A (Structure) for minimum thickness and compressive strength. Cavity walls require a minimum 50 mm cavity under Part C (Moisture), with 100 mm now standard for insulation under Part L (Energy Efficiency). Below-ground blockwork must use sulphate-resistant blocks in aggressive ground conditions.
How much mortar do I need for concrete blockwork?
Approximately 0.012 m³ of mortar per m² of standard blockwork with 10 mm joints - roughly half the mortar required for brickwork, as blocks cover a much larger face area. A standard mix for blockwork is 1 part cement to 5-6 parts soft sand by volume.