Construction Material Calculator
Estimate the quantities a build needs, from bricks and blocks to mortar and aggregate, with the wastage allowance that keeps you from a second delivery.
Formula
Volume = length × width × depth, then multiply by the yield per cubic metre
- Roughly 6.3 bags of cement per cubic metre of concrete mix
- Add about 10% for waste, settlement and spillage
A 3 × 2 m slab at 100 mm is 0.6 m³, needing about 4 bags of cement
Bricks and Blocks per Square Metre
Standard UK figures, based on a 10 mm mortar joint:
- Bricks (215 × 102.5 × 65 mm): 60 per m² in a single skin
- Concrete blocks (440 × 215 mm): 10 per m²
A cavity wall uses two skins, so double the brick count. Multiply your wall area by these figures and add wastage.
Mortar and Mixes
Roughly 1 m³ of mortar lays 1,000 bricks, so a typical wall needs about 0.06 m³ of mortar per square metre of single-skin brickwork.
Common mixes by volume:
- 1:5 or 1:6 cement to sand for general above-ground brickwork
- 1:4 for exposed or below-ground work needing more strength
- 1:3 for rendering
Stronger is not automatically better: mortar should be weaker than the units it joins, so that any movement cracks the joint rather than the brick.
Allow for Waste, and for Regulations
Add 5% for blocks and 5–10% for bricks, more if cutting around openings. Order in one delivery and check batch consistency, since brick colour varies noticeably between firings.
Structural work, foundations, load-bearing walls and anything affecting drainage or party walls falls under Building Regulations in the UK, and often needs approval and inspection. Treat these figures as estimating aids, not a substitute for a structural engineer or building control.
Quick Reference
| Material | Per m³ | For a 0.6 m³ slab |
|---|---|---|
| Cement (25 kg bags) | 6.3 bags | 4 bags |
| Sharp sand | 0.5 m³ | 0.3 m³ |
| Gravel or ballast | 0.75 m³ | 0.45 m³ |
| Water | ~150 litres | ~90 litres |
| Ready-mixed concrete | 1 m³ | 0.6 m³ plus 10% waste |
Frequently Asked Questions
- How many bricks per square metre?
- Sixty for a single skin with standard UK bricks and a 10 mm joint. A cavity wall with two skins needs 120.
- How much mortar do I need?
- Roughly one cubic metre per 1,000 bricks, or about 0.06 m³ per square metre of single-skin brickwork.
- What mortar mix should I use?
- 1:5 or 1:6 cement to sand for general brickwork, 1:4 where more strength is needed. Mortar should be weaker than the bricks it joins.
- Do I need building regulations approval?
- For structural work, foundations, load-bearing walls and anything affecting drainage or party walls, usually yes. Check with building control before starting.