All the examples below use the same garden wall: 20 ft long and 8 ft high, with one 3 × 7 ft door, built in US modular bricks (7⅝ × 2¼ in face) with ⅜ in mortar joints. Done correctly, that wall has 139 ft² of brickwork, needs 954 bricks, and you should order 1,049 with 10% waste.
1. Leaving out the mortar joint
This is the biggest single error. Each brick covers its own face plus a joint on its top and one on its end. If you divide the wall area by the bare brick face, you'll over-order by about a fifth.
| Brick | With joints | Without joints | Over-order |
|---|---|---|---|
| US modular (⅜ in joint) | 6.86 per ft² | 8.39 per ft² | +22% |
| UK standard (10 mm joint) | 59.3 per m² | 71.6 per m² | +21% |
| South Africa NFP (10 mm joint) | 51.9 per m² | 61.7 per m² | +19% |
On the example wall, forgetting the joints means ordering about 1,166 bricks instead of 954, more than 200 extra before waste. Fix: enter the joint thickness your bricklayer will use. The presets in our calculators already include it.
2. Mixing up nominal and actual brick sizes
US bricks are sold by a nominal size that already includes the joint: a modular brick is "8 × 4 × 2⅔ in", but the brick itself is 7⅝ × 3⅝ × 2¼ in. If you enter the nominal size and add a ⅜ in joint, you count the joint twice and under-order. If you enter the actual size with no joint, you over-order (mistake 1).
Fix: use the actual size plus your joint. Outside the US, quoted sizes such as 215 × 102.5 × 65 mm (UK) or 222 × 106 × 73 mm (South Africa) are already actual sizes. If in doubt, measure a brick from the pallet. The brick sizes chart lists both kinds of size.
3. Not subtracting doors and windows
Openings are brickwork you don't need. On the example wall, ignoring the door means pricing 160 ft² instead of 139 ft², about 144 extra bricks. On a house with a garage door and several windows, the difference runs into thousands.
Fix: subtract every opening, but keep a normal waste allowance: the cuts around openings are where most broken and offcut bricks come from.
4. Forgetting the wall is two bricks thick
A calculator assumes a single skin (one brick thick) unless you tell it otherwise. A one-brick (double-skin) wall, a cavity wall, or a typical 220 mm South African external wall uses two leaves, so twice the bricks. The example wall built double-skin needs about 1,908 bricks, not 954.
Fix: choose the right wall build. Free-standing garden walls over about 3 ft, load-bearing walls and most external walls are usually double. The brick calculator has a setting for it.
5. Mixing up feet, inches and meters
Typing a 20 ft wall as "20" while the calculator is set to meters makes it 20 m, more than three times longer, and the area about ten times larger. Typing inches into a feet box does the same in reverse.
Fix: check the unit switch before you start, and measure everything in one unit. A quick sanity check: a standard door is about 21 ft² or 1.9 m², so the wall area should look sensible next to that.
6. Measuring the wrong height
- Below-ground courses. Bricks usually start on the footing, below ground level. Measure from the top of the footing, not from the ground.
- Gable ends. The triangle under a pitched roof is half its base × its height. It's easy to leave out entirely. Our brick veneer calculator has a field for it.
- Copings and caps. A row of bricks on edge along the top of a garden wall is extra brickwork beyond the wall height.
7. Counting the corners twice
If you measure the outside length of every wall in a building, each corner gets counted twice: about one brick per course, per corner. That's small on a garden wall, but a few hundred bricks on a house. Fix: measure two opposite walls on the outside and the other two between them, or simply accept it as part of your waste allowance.
8. Skipping the waste allowance
The calculator's count is the bricks that end up in the wall. Real jobs also lose bricks to cuts, chips and breakages. The example wall needs 954 bricks, but you should order 1,049.
| Job | Typical waste |
|---|---|
| Straight wall with few openings | 5% |
| Wall with many openings or corners | 10% |
| Patio in herringbone or diagonal pattern | 10–15% |
| Reclaimed or second-hand bricks | 15–20% |
9. Ordering the exact number, from more than one batch
Brick colour varies between production batches. If you run short and the second delivery comes from a different batch, the patch can show for the life of the wall. Fix: order everything at once, round up to whole packs or pallets, and keep a few spares for future repairs.
10. Forgetting everything that isn't a brick
- Mortar: cement and sand. The dry mix is about 1.33 times the wet mortar volume, because it shrinks when water is added. The brick mortar calculator works this out.
- Wall ties for cavity walls and brick veneer, typically about 2.5 per m².
- Lintels over doors and windows, a damp-proof course, and delivery charges for bricks and sand.
Our brick wall cost calculator includes the mortar, ties and labor in one estimate.
11. Using wall bricks for a patio
Ordinary facing bricks aren't made to lie flat in the weather. Laid as paving, they can crack and flake in frost. For a patio or path, use clay or concrete pavers and the brick patio calculator, which uses paver sizes and a much thinner sand joint.
A quick checklist before you order
- Actual brick size entered, with the right joint thickness.
- Units checked: feet or meters, not a mix.
- Every wall, gable and below-ground course included.
- Doors, windows and garage doors subtracted.
- Single or double wall set correctly.
- Waste added, and the total rounded up to whole packs from one batch.
- Mortar, ties and lintels on the order too.
Estimates only. A calculator gives you a good order quantity, not a structural design. For load-bearing or retaining walls, check with a builder or engineer and your local building rules.
Frequently asked questions
What is the most common brick calculator mistake?
Leaving out the mortar joint. Dividing the wall area by the bare brick face over-orders by about 20%. For US modular bricks it gives 8.39 bricks per ft² instead of the correct 6.86.
Should I use the nominal or actual brick size?
The actual size, plus your joint thickness. US nominal sizes already include a ⅜ in joint, so adding a joint to them counts it twice.
How much extra brick should I order?
Usually 5% for a straight wall, 10% for walls with many openings or corners, 10–15% for patterned patios, and 15–20% for reclaimed bricks.
Do I subtract windows and doors when calculating bricks?
Yes. Subtract the area of every opening. Keep your normal waste allowance, because cuts around openings are where most waste comes from.
Why does my brick calculator give double the bricks?
It is probably set to a double-skin or cavity wall, which has two leaves of brick. A single-skin (half-brick) wall needs half as many.