How many blocks per m2?

Standard blocks (440mm × 215mm face) require 10 blocks per square metre of wall with 10mm mortar joints. This applies to both dense concrete blocks and aerated (aircrete) blocks. Add 10% for wastage and cuts. For a 10 m² wall, order 110 blocks. Foundation trench blocks are the same face size.

What mortar mix for blockwork?

Below ground (foundations): use a 1:3 cement:sand mortar or M6 designation. Above ground general use: 1:1:6 cement:lime:sand (M4) or 1:5 with plasticiser. Internal non-loadbearing: 1:2:9 (M2). Use sulphate-resistant cement in sulphate-bearing soils. Pre-mixed mortars in silos are increasingly popular for large projects.

How many wall ties do I need?

Standard wall ties are placed at 900mm horizontal and 450mm vertical centres, giving approximately 2.5 ties per m² of wall. Around openings, ties should be at maximum 300mm centres within 225mm of the reveal. Stainless steel ties (to BS EN 845-1) are required in exposed locations and are recommended everywhere in the UK.

Where does DPC go in a blockwork wall?

A DPC (damp-proof course) is laid at minimum 150mm above external ground level in the inner and outer leaves. It must be a continuous horizontal barrier of polyethylene or bitumen-based sheet. The DPC laps with the DPM (damp-proof membrane) in the floor slab. Additional DPC is needed at sills and thresholds.

What is the difference between dense and aerated blocks?

Dense concrete blocks (7.3 N/mm²) are heavy, strong and used below ground, for load-bearing walls and fire walls. Aerated blocks (aircrete, e.g., Thermalite at 3.6 N/mm²) are lightweight, provide better insulation and are used for the inner leaf of cavity walls above ground. Dense blocks are typically grey; aerated blocks are white/cream.

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Blockwork Wall Calculator — Blocks, Mortar & Wall Ties

Calculate blocks per m2, mortar, wall ties and DPC for blockwork wall construction.

Wall Length

Wall Height

Block Type

Block Price

Openings Area

Total area of windows/doors

How We Calculate This

This calculator determines block quantities, mortar, wall ties and DPC for blockwork wall construction.

Block count

Net Area = (Wall Length × Height) - Openings
Blocks = Net Area × 10 blocks/m² × 1.1 (wastage)
Standard block face: 440mm × 215mm with 10mm mortar joints.

Wall ties

Ties = (Length / 900mm) × (Height / 450mm)
At 900mm horizontal × 450mm vertical centres = ~2.5 ties/m².

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.