How many bricks for a wall:
an estimate from area, brick module and waste

Start with the brick module, not the brick

The quickest way to estimate bricks for a wall is to divide the wall's volume by the volume of one brick including the mortar around it. That 'brick plus joint' size is called the module. A common modular brick measures about 190 × 90 × 90 mm; with a 10 mm mortar joint it occupies a 200 × 100 × 100 mm space, which is 0.2 × 0.1 × 0.1 = 0.002 m³.

Because the module already includes mortar, you do not add a separate allowance for joints. You just divide space by space. That makes the result a good first figure for ordering, and a number to refine for the real brick size, bond pattern and wall details.

A first worked example

A second route gives the same result and is easier on site. The wall face is 4 × 3 = 12 m², and one brick's face on the wall, laid lengthwise, covers 0.2 × 0.1 = 0.02 m² including mortar. 12 ÷ 0.02 = 600. For a 100 mm wall, which is one brick wide, that is exactly 50 bricks per square metre of wall face.

The count per cubic metre never changes, as it is just 1 ÷ 0.002. The thickness changes only the count per square metre.

Deducting doors and windows

Openings contain no brickwork, so remove their area before you divide. A standard door of 1.0 × 2.1 m takes out 2.1 m², and a window of 1.5 × 1.2 m takes out 1.8 m². Small openings of under about 0.1 m² are usually ignored in estimating, since the cut bricks around them offset the saving.

Lintels and sill bands bring some brick area back, because cut and special bricks fill the space above and below the frame. Treat the deduction as an estimate and keep the margin below to cover it.

Wastage, breakage and what to order

Bricks chip during unloading, stacking and cutting. A common allowance is 5% for good-quality burnt clay bricks, rising to 8 to 10% for softer bricks, long hauls or complicated bonds. Apply it to the net figure.

• Net bricks: 405
• Allowance at 5%: 405 × 1.05 = 425.25
• Order: 426 bricks, usually rounded up to a convenient 430 or 450 for delivery
• For a 10% allowance the order is 405 × 1.10 = 445.5, so 446

Leave out any allowance for the bricks you will cut for corners and openings, since they are covered by this margin. If the supplier sells in thousands, pick up the count from the partial load rather than ordering an extra thousand, and keep a small number for later repairs.

How much of the wall is mortar?

The 10 mm joints take up a surprising share of the wall. A 190 × 90 × 90 mm brick has a real volume of 0.19 × 0.09 × 0.09 = 0.001539 m³, so 600 bricks occupy 0.9234 m³. The wall volume is 1.2 m³, which leaves 1.2 − 0.9234 = 0.2766 m³ for mortar, about 23% of the wall.

That is the wet volume of mortar that sits in the joints. The dry materials you need to mix are more, since sand and cement fill their own voids when wetted; a factor of roughly 1.25 to 1.33 is typical, and the mortar mix (for example 1:4 or 1:6 cement to sand) decides the cement bag count. Add extra for waste on the mixing board and for plaster if you are estimating the whole job.

Scaling up: four walls of a small room

The same method extends to a store room built with 100 mm walls, 4 m by 3 m inside, and 3 m high. The perimeter is 2 × (4 + 3) = 14 m, so the wall face is 14 × 3 = 42 m². With a door of 2.1 m² and two windows of 1.8 m² each, the net area is 42 − 2.1 − 3.6 = 36.3 m².

At 50 bricks per square metre, the net count is 36.3 × 50 = 1,815 bricks, and with a 5% allowance the order is 1,905.75, or about 1,906 bricks. Note how little the openings change the total: they remove 5.7 m² out of 42, about 14%. Bigger rooms spend a smaller share of their walls on openings, so apply the same deduction method rather than a flat percentage.

Corners are the other detail. Wall lengths measured on the centre line avoid counting the corner bricks twice, while lengths measured on the outside do count them twice. On a small room the difference is a few bricks per corner, and it is covered by the wastage margin, but on a long building it is worth measuring along the centre line.

Where the estimate can go wrong

• Different brick sizes: country bricks and older moulds are often larger than the modular size; use the actual size plus 10 mm.
• Wrong thickness: a 100 mm partition and a 200 mm external wall differ by a factor of two.
• Bond pattern: stretcher and header patterns use more bricks per metre of face in thicker walls.
• Cavity walls count both leaves; do not use the overall thickness.
• Gable walls and parapets are not rectangles; split them into rectangles and triangles.

A brick quantity calculator gives you the repeated arithmetic quickly, but the inputs, brick size, thickness and openings, come from drawings and a tape measure. Verify them on site, and ask your mason what allowance they expect for their brick, since it differs from place to place.