Block Calculator — How Many Blocks Do I Need?

This calculator works out the number of concrete blocks needed by calculating the total wall area, subtracting any door and window openings, then multiplying by the blocks-per-square-metre rate.

The formula

Blocks = (Wall area - Openings) × 10 blocks/m² × Wastage factor

Standard UK blocks are 440 × 215mm face size. With 10mm mortar joints, the working size is 450 × 225mm, giving exactly 10 blocks per square metre.

Opening deductions

• Standard door: 1.8 m² (a typical structural opening of roughly 900mm × 2000mm for a single internal door)
• Standard window: 1.2 m² (approximately 1200mm × 1000mm)

Standards

Block sizes conform to BS EN 771-3 (Specification for masonry units — Aggregate concrete masonry units). Mortar should comply with BS EN 998-2 and be appropriate to the exposure conditions, with masonry designed to BS EN 1996 (Eurocode 6, the current UK masonry design code that superseded the withdrawn BS 5628 suite in 2010).