How to use it
- Measure the wall length and height, and add up the area of the openings.
- Choose the Brick or block and check its size on the packaging or the data sheet.
- Enter the Mortar joint the unit is laid with, and the Waste allowance.
- Read Bricks or blocks to order and Mortar for the joints.
How the number of units is worked out
A square metre of wall takes as many units as fit in it with the joints around each one. The joint is added to the length and to the height of the unit, so a 215 × 65 mm brick with a 10 mm joint covers 225 × 75 mm.
The net area is the wall area less the openings. It is multiplied by the units per square metre and by the waste, then rounded up to whole units.
units per m² = 1 000 000 ÷ [(length + joint) × (height + joint)]
units to order = net area × units per m² × (1 + waste), rounded upMortar
The mortar fills the joints. The volume of a wall one unit thick, less the volume of the units in it, is the mortar: for each square metre it is the thickness times the share of the face that is joint.
The figure is a theoretical volume for the joints. Real mortar is lost on the trowel and to uneven faces, so order a little more than the figure, as the mortar maker's yield for the wall suggests.
mortar per m² = thickness × [1 − length × height ÷ ((length + joint) × (height + joint))]What this calculator does not include
- Lintels over the openings, bond patterns, reinforcement and the wall ties.
- Cutting for corners and the mortar that a thin-bed adhesive or a different mortar needs.
- Walls that are not a single unit thick, such as a cavity wall, which needs the thickness of each leaf.
Worked example: a 6 m × 2.7 m wall with 2 m² of openings, 60 cm aerated blocks 15 cm thick
The net area is 6 × 2.7 − 2 = 14.20 m². With a 10 mm joint one block covers 610 × 260 mm, so 6.31 blocks fit in each square metre.
14.20 × 6.305 = 89.5, and with 5 % waste 94.0, so 95 blocks. The mortar is 0.115 m³.
| Aerated 15 cm | Standard brick | |
|---|---|---|
| Units per m² | 6.3 | 59.3 |
| Units to order (5 % waste) | 95 | 884 |
| Mortar | 0.115 m³ | 0.250 m³ |
Frequently asked questions
How many bricks are in a square metre of wall?
A standard 215 × 65 mm brick with a 10 mm joint covers 225 × 75 mm, so about 59 fit in a square metre of wall. The same brick with a 0 mm joint would give about 72 per square metre.
How much mortar do I need for a brick wall?
The theoretical joint volume of a 102.5 mm standard brick wall is about 0.018 m³ per square metre, which is 0.25 m³ for 14.2 m². Order a little more, because mortar is lost to waste on site.
Why do aerated blocks need less mortar?
The blocks are large and thick, so the joints take a smaller share of the face. Aerated blocks are often laid with a thin-bed adhesive instead of mortar, which needs a much narrower joint, so check the joint width on the data sheet.
Should I add waste to the bricks?
Yes. Some units break, and cuts at the openings and at the ends of the wall use up whole units. 5 % is a common allowance; use more for a complicated wall.
Does the tool store what I enter?
No. The calculation runs in your browser and nothing you type is sent to us or stored.
Sources
- Wikipedia: Brick (standard UK and US modular sizes and the 10 mm mortar joint)
- Türk Ytong: Ytong wall blocks, 60 × 25 cm face in thicknesses of 10 to 40 cm
Figures and text last checked on Tuesday, November 10, 2026.