How many blocks do I need per square metre?

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.

What is the standard block size in the UK?

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.

How much mortar do I need for blockwork?

You need approximately 0.012 m³ of mortar per square metre of blockwork with 10mm joints. For a typical wall of 10 m², that works out to around 0.12 m³ of mortar, which is roughly 1 bag of cement and 100kg of building sand using a 1:4 mix.

Should I use 100mm or 140mm blocks?

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.

How many blocks come on a pallet?

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.

Block Calculator — How Many Blocks Do I Need?

Calculate the number of concrete blocks needed for any wall. Accounts for openings, mortar joints, and standard UK block sizes.

Wall Length

Average length per wall

Wall Height

Standard storey height is 2.4m

Number of Walls

Block Size

All sizes give 10 blocks per m² with 10mm mortar joints

Subtract Openings

Number of Doors

Each door deducts ~1.8 m²

Number of Windows

Each window deducts ~1.2 m²

Include wastage allowance

Adds 10% extra for cutting and breakage

Wastage Percentage

10% standard for blockwork; increase for complex layouts

Price Per Block (optional)

Enter your supplier price for a cost estimate

How We Calculate This

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 (approximately 838mm × 2040mm frame opening)
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 as specified in BS 5628 / Eurocode 6.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Verify with your supplier.