Brick & Block Calculator UK - How Many Bricks or Blocks Do I Need?

How Many Bricks Do I Need Per m²?

The answer depends entirely on bond, not brick size alone. For a standard UK brick (215 × 102.5 × 65mm) with a 10mm mortar joint, the coordinating size once bedded is 225 × 75mm. Divide 1m² by that face area and you get almost exactly 60 bricks - the reason 60 bricks per m² is the universal trade figure for stretcher bond, the pattern used in cavity wall outer leaves, garden walls and most everyday brickwork.

English and Flemish bond both need a solid one-brick (215mm) wall, since headers have to run through the full thickness to tie it together. Working headers into every course (English) or every brick (Flemish) roughly doubles the unit count to 120 bricks per m², even though the wall is only twice as thick, not twice as tall or long - the header courses use noticeably more brick per m² of visible face than a simple doubling of the stretcher-bond count would suggest.

Bond Types and What Each Is For

• Stretcher bond - every brick shows its long face, each course offset by half a brick from the one below. The standard for cavity wall leaves, garden walls and anywhere a half-brick (102.5mm) wall is adequate. 60 bricks per m².
• English bond - whole courses of stretchers alternating with whole courses of headers. The strongest traditional bond, since headers tie right through a one-brick wall, but it uses the most facing bricks. 120 bricks per m².
• Flemish bond - stretcher and header alternate within every course, each header centred over the stretcher below. Slightly weaker than English bond but a more even, decorative appearance, historically the more expensive bond to lay well since more mitred cuts and half-bricks are needed. Also 120 bricks per m².

Both English and Flemish need a genuine one-brick (215mm) solid wall - there's no way to work headers through a half-brick or cavity leaf, since there's nothing on the other side for them to tie into.

Mortar Quantities and Mix Ratios

A half-brick stretcher-bond wall with 10mm joints needs roughly 0.025 m³ of wet mortar per m². A solid one-brick wall (English or Flemish) needs roughly double that, since it's twice the depth with a similar joint density. These figures match our mortar calculator, which uses the same brick geometry and bulking factor.

Mix ratio is chosen by exposure and brick strength, not bond: 1:4 for general load-bearing work without a plasticiser, 1:5 for the most common general-purpose mix with a plasticiser, 1:6 for soft old bricks that would crack under a stronger mix. See our mortar calculator for the full breakdown by mix ratio, or use the mortar figures this calculator gives you directly.

Block Types: Dense vs Aerated vs Hollow

• Dense concrete block - heavy (around 2,000 kg/m³), strong, and the standard choice below damp-proof course, for load-bearing work, and anywhere fixings need something solid to bite into. Poor insulator on its own.
• Aerated / thermal block (aircrete, e.g. Thermalite or Celcon) - much lighter (roughly 600 kg/m³), easy to cut with a hand saw, and a far better insulator. The standard choice for the inner leaf of a modern cavity wall above DPC, usually paired with cavity insulation.
• Hollow block - lighter than dense block by leaving voids in the unit, sometimes filled with concrete and reinforcement on site for extra strength. Mainly seen in retaining structures and some foundation work rather than general walling.

Whichever type, a standard 440 × 215mm block gives 10 blocks per m² with a 10mm joint - thickness (100mm, 140mm, 215mm) changes the wall's depth, mortar volume and weight, not the block count per m² of face area.

Cavity Walls and Wall Ties

A modern UK cavity wall is normally a brick outer leaf (stretcher bond, 102.5mm) and a block inner leaf (aerated block, 100mm), with a clear cavity between them, often filled with insulation. The two leaves are tied together with wall ties so they act as one structural wall rather than two independent skins.

UK guidance (Approved Document A, referencing BS 8000-3) specifies wall ties at 900mm horizontal by 450mm vertical centres, staggered, which works out to 2.5 ties per m². Around openings, ties need to be closer: no more than 300mm vertically, and within 225mm of the vertical edges of the opening.

This calculator works out ties for one leaf at a time. If you're pricing a full cavity wall (brick outer, block inner), run the calculator once for each leaf, but only include wall ties in one of the two runs - they tie the two leaves together, so counting them on both sides would double the real number.

Bricks and Blocks by Area: Quick Reference

Standard UK brick, 10mm joints, 5% waste, figures regenerated directly from the calculator above.

Use the calculator above for openings, custom sizes and mortar. Travis Perkins and Jewson both sell facing bricks in packs of around 500 and dense blocks in packs of around 72 for trade collection, while Wickes and B&Q stock smaller quantities more suited to DIY-scale jobs. Pack sizes vary by manufacturer and product, so confirm with your supplier before ordering.

Frequently Asked Questions

How many bricks do I need per m2?

60 bricks per m² for a standard UK brick (215 × 102.5 × 65mm) with 10mm joints in stretcher bond, the bond used for cavity wall outer leaves, garden walls and most modern brickwork. A solid one-brick wall in English or Flemish bond needs 120 bricks per m², since headers are worked into every course rather than a simple running pattern.

How many blocks do I need per m2?

10 blocks per m² for a standard 440 × 215mm block with 10mm joints, whatever the block's thickness. Thickness changes the depth of the wall and how much mortar and how many wall ties you need, not how many blocks cover the face area.

What's the difference between stretcher, English and Flemish bond?

Stretcher bond shows every brick's long face and staggers each course by half a brick: the standard for a half-brick (102.5mm) wall or a cavity leaf. English bond alternates whole courses of stretchers and whole courses of headers (the brick's end face). Flemish bond alternates stretcher and header within every course. Both English and Flemish need a solid one-brick (215mm) wall to tie the headers through, and both use 120 bricks per m² against stretcher's 60.

How much mortar do I need for a brick wall?

Around 0.025 m³ of wet mortar per m² for a half-brick stretcher-bond wall with 10mm joints, roughly double that for a solid one-brick wall. At a 1:5 mix that's about 0.4 bags of cement and 43kg of sand per m², once dry sand bulking against mixed wet mortar is accounted for. This matches our mortar calculator, which uses the same figures.

Do I need wall ties for a cavity wall?

Yes. UK guidance (Approved Document A, referencing BS 8000-3) calls for 2.5 wall ties per m², spaced at 900mm horizontally and 450mm vertically in a staggered pattern, with closer spacing (300mm vertically, within 225mm of the opening) around doors and windows.

Dense block or aerated block - which do I need?

Dense concrete block is heavier and stronger, used below damp-proof course, in load-bearing situations and where fixings need to bite into something solid. Aerated (thermal) block is lighter, easier to cut, and gives much better insulation, which is why it's the standard choice for the inner leaf of a modern cavity wall above DPC. Hollow blocks trade some strength for weight and are mainly used where they'll be reinforced and filled, such as some retaining or foundation work.