How Many Blocks for a Wall?

How We Calculated This

Standard UK concrete blocks measure 440mm x 215mm (face dimensions). With a 10mm mortar joint, the working size becomes 450mm x 225mm.

This gives a coverage rate of 10 blocks per m²:

• Each block covers: 0.45m x 0.225m = 0.10125m²
• Blocks per m²: 1 ÷ 0.10125 = 9.88, rounded to 10

For a 5m x 2.4m wall:

• Wall area: 5 x 2.4 = 12m²
• Blocks needed (no wastage): 12 x 10 = 120 blocks
• With 10% wastage: 120 x 1.10 = 132 blocks

Common Block Types

• Dense concrete blocks (7.3N/mm²): ~20kg each, used below DPC and for structural walls
• Medium-density blocks (3.6N/mm²): ~15kg each, general-purpose inner leaf
• Lightweight aerated blocks (e.g. Celcon/Thermalite): ~8kg each, good insulation, inner leaf of cavity walls

All these types use the same 440 x 215mm face dimensions, so the coverage rate of 10/m² applies to all of them.

Block Thickness

The most common thicknesses in the UK are:

• 100mm: Standard single-skin walls, inner leaf of cavity walls
• 140mm: Thicker inner leaf for additional strength or insulation
• 215mm: Solid blockwork walls (less common in modern construction)

Mortar Requirements

For blockwork you need approximately 0.012m³ of mortar per m². For 12m² of wall:

• Mortar volume: 12 x 0.012 = 0.144m³
• Using a 1:5 cement:sand mix: roughly 1 bag of cement (25kg) and 6–7 bags of building sand (25kg)

Tips

Blocks are sold in pallet quantities — typically 72 blocks per palletfor 100mm dense blocks. For 132 blocks, you would need 2 pallets. Always check the number per pallet when ordering, as it varies by block type and manufacturer.

Use a string line and profile boards for accuracy. Lay blocks on a full mortar bed and butter the ends. Check level and plumb every 2–3 courses.