Brickwork is one of the largest cost items in a low-rise building, and it is also one of the easiest to over-order or under-order. A single wall may look simple on the drawing, but the number of bricks, the cement and sand for the mortar, and the extra material for plaster all need to be worked out separately and added together. This article shows exactly how to calculate the number of bricks in a wall, the mortar needed to lay them, and the plaster that goes on top, with a fully worked example and the common mistakes to avoid.
If you would like to check your own numbers while reading, keep the Brick Calculator and the Plastering Calculator open in another tab. Both tools show the same steps that we describe here.
1. Start with the wall, not the brick
The first step is to find the net volume of the wall. Measure the length and height of each wall panel, multiply them to get the area, and subtract openings such as doors and windows. Then multiply by the thickness of the wall. Wall thickness is where many beginners make mistakes, because walls are named by the brick's dimension that faces the thickness:
- A half-brick wall (about 4.5 inches or 115 mm thick) is made with bricks laid as stretchers. It is used for partition walls.
- A one-brick wall (about 9 inches or 230 mm thick) is made with bricks laid in a header and stretcher pattern. It is used for external and load-bearing walls.
Thickness measured on the finished wall includes the mortar joints, so always use the actual wall thickness from the drawing, usually 4.5 inches or 9 inches in this region.
2. The size of one brick and the mortar joint
Brick sizes are not the same everywhere. A common traditional size is 9 × 4.5 × 3 inches, which is about 228 × 114 × 76 mm. Other sizes used in practice include 190 × 90 × 90 mm modular bricks and 215 × 102.5 × 65 mm standard bricks. Always check the size of the bricks you will actually buy, because a difference of even 5 mm in one dimension changes the count noticeably across a large wall.
Mortar joints are normally about 10 mm thick, both horizontally (bed joints) and vertically (perpend joints). To count bricks, we use the size of a brick together with its share of mortar. In effect, each brick occupies a block of space slightly larger than itself: (length + joint) × (width + joint) × (height + joint).
3. The brick count formula
Number of bricks = wall volume ÷ volume of one brick with its mortar joint.
For a 228 × 114 × 76 mm brick with a 10 mm joint, the brick-plus-mortar size is 238 × 124 × 86 mm. Converting to metres, this is 0.238 × 0.124 × 0.086 = 0.002538 m³ per brick.
If the wall volume is 4.248 m³ (which is 150 cubic feet, for example a 9-inch wall of 200 square feet net area), the number of bricks is 4.248 ÷ 0.002538 = 1,674. With a 5 percent wastage allowance, you should order about 1,758 bricks. Those are the same numbers you will see in the Brick Calculator with its sample values.
4. A quick rule of thumb for checking
For the traditional brick size with 10 mm joints, one cubic metre of brickwork contains about 394 bricks (1 ÷ 0.002538), which is about 11 bricks per cubic foot of wall. This is a handy check. If your calculation gives a number far from that for the same brick size, recheck the brick size, the joint thickness and the wall thickness.
5. The mortar needed for the wall
Mortar fills the space between bricks. The simplest way to find its volume is to subtract the volume of the bricks themselves from the wall volume:
- Volume of the bricks alone = number of bricks × 0.228 × 0.114 × 0.076 = 1,674 × 0.001975 = 3.307 m³
- Wet mortar volume = 4.248 − 3.307 = 0.941 m³
So in a typical wall with 10 mm joints, mortar makes up roughly one fifth of the wall volume (here, 22 percent). That is much higher than many people expect, which is why mortar quantities can be a significant cost.
6. From wet mortar to dry materials
Just like concrete, mortar needs more dry material than the finished volume of wet mortar, because the cement fills the voids between sand grains. For mortar, a dry volume factor of about 1.27 is commonly used. So:
- Dry volume = 0.941 × 1.27 = 1.196 m³
For a 1:6 mix (one part cement to six parts sand), the sum of parts is 7:
- Cement volume = 1.196 ÷ 7 = 0.1709 m³
- Cement mass = 0.1709 × 1440 kg/m³ = 246 kg, or 4.9 bags of 50 kg
- Sand = 1.196 × 6 ÷ 7 = 1.025 m³, or about 36 cubic feet
That is the full set of materials for 1,674 bricks laid in a 1:6 mortar: roughly five bags of cement and one cubic metre of sand. Remember to add wastage to the mortar too, since some mortar always falls on the ground, dries in the tray, or is used for pointing and levelling.
7. Choosing the mortar ratio
The mortar ratio should match the wall type and the specification. Typical choices are:
- 1:6 for ordinary non-load-bearing partition walls and boundary walls
- 1:5 for standard load-bearing walls in small buildings
- 1:4 for stronger masonry, plinth work and walls exposed to heavy moisture
A richer mortar gives higher strength and better bond but costs more and can crack from shrinkage if over-rich. A leaner mortar saves cement but may give weaker walls and poorer bond. Follow the drawings and local code rather than choosing a ratio only on price.
8. The effect of changing brick size or joint thickness
It is worth experimenting with the numbers to see how sensitive the estimate is.
- With a thicker joint of 15 mm instead of 10 mm, the brick-plus-mortar size becomes 243 × 129 × 91 mm, or 0.002853 m³. Bricks per cubic metre drop from 394 to 350, but mortar volume rises sharply.
- With larger bricks, fewer are needed, and the total length of joint falls, so mortar use per cubic metre of wall falls.
- With modular 190 × 90 × 90 mm bricks and a 10 mm joint, the unit is 200 × 100 × 100 mm = 0.002 m³, giving exactly 500 bricks per cubic metre.
These comparisons show why a supplier's brick size and the mason's joint thickness have a direct effect on cost. In the Brick Calculator you can pick one of the standard brick sizes or enter a custom size, and also change the mortar joint, wastage, mortar ratio and dry volume factor.
9. Plaster: the next layer of material
After brickwork comes plaster. Walls are usually plastered on both faces with 12 mm (half-inch) cement-sand plaster; ceilings use a thinner coat of about 6 to 8 mm. The method is the same as for mortar: find the wet volume, convert to dry volume with the factor of 1.27, and divide it by the mix parts.
For 500 square feet of wall (46.45 m²) and a thickness of 12.7 mm (half an inch):
- Wet volume = 46.45 × 0.0127 = 0.590 m³
- Dry volume = 0.590 × 1.27 = 0.749 m³
- For a 1:4 mix: cement = 0.749 ÷ 5 = 0.1498 m³ = 216 kg = 4.3 bags
- Sand = 0.749 × 4 ÷ 5 = 0.599 m³ = 21 cubic feet
You can check these figures directly with the Plastering Calculator. Remember that real plaster thickness is almost never exactly the design value: brickwork is not perfectly flat, so plaster fills depressions and uses more material than the theoretical figure. A wastage of 10 percent or more is common for plaster, especially on rough walls.
10. Plaster area for a room
To find the plaster area of a room, add the area of all four walls (perimeter × height), subtract door and window openings, and add the area of the ceiling if it is to be plastered. If walls are plastered on both sides, repeat for the outside faces. It helps to make a small table listing each wall, its length, height, deductions and net area, so that nothing is forgotten.
11. Other masonry units
The same principles apply when you build with concrete blocks, which are larger and quicker to lay. Fewer joints mean less mortar per square metre of wall. Use the Concrete Block Calculator for blocks, and our Precast Compound Wall Calculator if you are fencing a plot with precast panels instead of brickwork.
12. Brick quality checks before you buy
An estimate is only useful if the bricks are good. Before accepting a delivery, do these simple checks:
- Shape and size. Bricks should be uniform, with straight edges and sharp corners. Measure a sample of 20 bricks laid end to end to check consistency.
- Colour and sound. Well-burnt bricks have an even colour and give a clear metallic ring when two are struck together. A dull thud suggests under-burning.
- Water absorption. A good brick absorbs a limited amount of water. Soak a brick for 24 hours and compare weights; large increases indicate a porous brick that will absorb mortar water and weaken the bond.
- Efflorescence. White salt marks on a soaked and dried brick indicate soluble salts that will stain plaster.
- Compressive strength. For load-bearing walls, ask for test reports.
Brick breakage during transport is real: the 5 percent wastage in our estimate is a typical starting point, but poor quality or long transport can push it to 10 percent.
13. Soaking bricks and mortar mixing tips
Dry bricks pull water out of fresh mortar and can leave a weak bond. Soak clay bricks in clean water for a few hours before laying so that they are damp but surface-dry when used. Mix mortar in small batches that can be used within about an hour, and never re-temper mortar that has started to set. Keep the sand clean and free from clay lumps, and measure cement and sand by volume with a standard box so that the ratio is consistent.
14. Putting it all together: a worked bill of materials
For the 200 square foot, 9-inch wall used in our example, with plaster on both faces (400 square feet of plaster), the combined requirement would be approximately:
- Bricks: about 1,760 (including 5 percent wastage)
- Mortar cement (1:6): about 5 bags
- Mortar sand: about 1.0 m³ (36 cft)
- Plaster cement (1:4, half inch): about 3.4 bags for 400 sq ft
- Plaster sand: about 0.48 m³ (17 cft)
Adding wastage for mortar and plaster and rounding up to whole bags gives practical order quantities. This sort of bill of materials is exactly what a contractor needs to price the job and what an owner needs to check a quotation.
Frequently asked questions
How many bricks are needed for 100 square feet of wall?
For a 9-inch (one brick) thick wall, 100 square feet has a volume of 75 cubic feet, which needs about 840 bricks of 228 × 114 × 76 mm with 10 mm joints. For a 4.5-inch wall, about 420 bricks are needed. Add wastage on top.
Why is my brick count different from my mason's number?
Masons often use rules of thumb based on local bricks and joint thickness. Differences usually come from brick size, joint thickness, wall thickness and whether openings were deducted. Compare each input before assuming either figure is wrong.
Do I add mortar for plaster to the mortar for brickwork?
Yes. Brickwork mortar and plaster are separate quantities, often with different mix ratios, so calculate each one and add the cement and sand totals.
What is the dry volume factor for mortar?
About 1.27 is widely used for cement-sand mortar. It converts the volume of wet mortar into the loose volume of cement and sand required.
How much wastage should I allow for bricks?
Five percent is a common allowance. Use more for poorly burnt bricks, long hauling, or complex walls with many cuts.
Final thoughts
The logic of a brickwork estimate is straightforward once it is broken into steps: wall volume, bricks, mortar, then plaster. Each step uses a simple formula and a few assumptions that you can verify on site. By understanding those steps, you will be able to read any quotation critically, negotiate with confidence, and catch mistakes before materials are ordered. Use the calculators to save time, but keep the method in mind so you can always check the result yourself.
Disclaimer: Estimates in this article are for general guidance. Always follow the project drawings, specifications and local building code, and have final quantities confirmed by a qualified engineer.
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