Block Calculator — How Many Blocks Do I Need?

For standard 440 × 215mm blocks with 10mm mortar joints, you need 10 blocks per m². This applies to all standard block thicknesses (100mm, 140mm, 200mm) as the face dimensions remain the same. Always add 10% for wastage and cutting.

The standard UK concrete block is 440 × 215 × 100mm (work size including mortar joints is 450 × 225mm). Other common thicknesses are 140mm for cavity wall inner leaves and 200mm for foundation blockwork. All conform to BS EN 771-3.

For 100mm blockwork with 10mm joints you need approximately 0.012 m³ of mortar per m². Thicker blocks need more (about 0.016 m³/m² for 140mm and 0.024 m³/m² for 200mm) because the bed and perpend joints run the full block width. For a typical 100mm wall of 10 m², that is around 0.12 m³ of mortar — roughly 2 × 25kg bags of cement and about 180kg of building sand using a 1:4 mix. Use our Mortar Calculator for the exact cement and sand split, which depends on the yield convention used.

For internal partition walls, 100mm blocks are standard. For the inner leaf of cavity walls, 140mm blocks are commonly used in new-build construction to meet thermal and structural requirements. For foundation walls below DPC, 200mm dense blocks are typical. Check your plans or Building Control for the required specification.

A standard pallet of 100mm blocks typically contains 72 blocks (enough for about 7.2 m² of wall). Pallet quantities vary by supplier and block type. When ordering, round up to full pallets to reduce cost per block and minimise delivery charges.