Build It Brick Calculator: How It Works

The Build It brick calculator works out how many bricks you need for a wall (or similar structure) from the wall’s dimensions, the brick size, and the mortar joint thickness. You enter length and height (and optionally wall thickness for cavity or double-skin walls) and get back the brick count, plus area and mortar volume. It is a straightforward area-based estimate that assumes standard brick dimensions and a uniform bed joint.

Formula

The calculator uses the standard brickwork formula: first find how many bricks fit along the length and how many courses (rows) fit up the height, then multiply. The key is that the mortar joint is added to the brick dimension in each direction.

• Bricks per course = floor( (length in mm) / (brick length + joint) )
• Number of courses = floor( (height in mm) / (brick depth + joint) )
• Total bricks = bricks per course × number of courses

Where:

• Length (l) – horizontal wall length in meters (convert to mm by ×1000).
• Height (h) – vertical wall height in meters (×1000 for mm).
• Brick length (b) – the longer face dimension in millimeters (typically 215 mm in the UK, 8 in in the US).
• Brick depth (d) – the height of the brick in millimeters (typically 65 mm in the UK, 2.25 in in the US).
• Mortar joint (j) – the bed and perpend joint thickness in millimeters (usually 10 mm).

The result is rounded up to the nearest whole brick because you cannot order a fraction of a brick.

Worked Example

Using the default values: wall length 5 m, height 2.4 m, brick length 215 mm, brick depth 102.5 mm (a standard UK brick laid flat), and 10 mm mortar joint.

1. Convert wall to mm: 5 m = 5000 mm, 2.4 m = 2400 mm.
2. Bricks per course = 5000 / (215 + 10) = 5000 / 225 = 22.22 → 23 bricks (rounded up).
3. Number of courses = 2400 / (102.5 + 10) = 2400 / 112.5 = 21.33 → 22 courses.
4. Total bricks = 23 × 22 = 506 bricks.

The calculator gives 506 bricks, which matches the manual calculation. Note that the wall area is 5 × 2.4 = 12 m², so this is roughly 42 bricks per m² – a common figure for standard brickwork.

When to Use the Brick Calculator

Use this calculator for planning a new wall, extension, garden wall, or any brick structure where you need a quick material estimate. It is especially useful for:

• Estimating how many bricks to order for a project.
• Comparing brick sizes or joint thicknesses.
• Getting a rough cost estimate by multiplying the brick count by the local brick price.

The calculator assumes a single-skin (half-brick thick) wall. For a full-brick (one-brick thick) wall, double the result. For a cavity wall, double again if both leaves are half-brick. Always add a wastage allowance – typically 5–10% – for cutting and breakage.

How to Choose the Right Brick Size

Brick dimensions vary by region and type. In the UK, the standard brick is 215 mm × 102.5 mm × 65 mm (length × depth × height). In the US, a standard modular brick is 8 in × 3.5 in × 2.25 in (actual dimensions, but with mortar the nominal size becomes 8 × 4 × 2.67 in).

When entering dimensions, always use the actual brick size, not the nominal size that includes mortar. If you are using metric bricks, enter millimeters. For imperial bricks, convert to millimeters (1 inch = 25.4 mm) or use the calculator with imperial units if available. The calculator above uses millimeters for brick dimensions and meters for wall dimensions – be consistent.

If you are using a non-standard brick (e.g., a thin brick veneer or a large block), adjust the dimensions accordingly. The formula works for any rectangular unit, but the result will only be accurate if the brick dimensions are correct.

Common Mistakes and How to Avoid Them

Several errors can throw off your brick count:

• Unit mix-ups: mixing meters and millimeters without converting. Always convert wall dimensions to mm before dividing.
• Forgetting the mortar joint: using the brick size alone (without adding the joint) overestimates the brick count because bricks are closer together.
• Rounding too early: rounding each division to a whole number before multiplying can introduce errors. Keep fractional values until the final multiplication, then round up.
• Ignoring wastage: bricks break, and you need to cut bricks at corners and openings. Add 5–10% to the total.
• Not accounting for openings: if your wall has windows or doors, subtract their area from the wall area first, or calculate the bricks for the solid sections separately.

For example, if you have a 1 m × 1 m window in the 5 m × 2.4 m wall, the net area is 12 – 1 = 11 m². At 42 bricks/m², that is 462 bricks, not 506. Always subtract openings for a more accurate estimate.

Limitations of the Formula

The area-based method assumes a perfectly rectangular wall with no openings, no corners, and no special brick patterns. In reality, you will need extra bricks for:

• Corners and returns (where walls meet).
• Lintels over openings.
• Cut bricks at edges and around openings.
• Bond patterns (e.g., Flemish bond uses more half-bricks than stretcher bond).

The calculator also ignores the thickness of the wall. A half-brick wall (102.5 mm thick) uses one brick per course; a one-brick wall (215 mm thick) uses two bricks per course, so the count doubles. Cavity walls with two leaves also double the count. Adjust accordingly.

Finally, the mortar volume calculation is approximate – it assumes the mortar fills the joints completely and ignores waste. In practice, you will need more mortar due to spillage and overfill. Order 10–15% extra mortar mix.

Frequently Asked Questions

How many bricks are in a square meter?

For standard UK bricks (215 × 102.5 × 65 mm) with a 10 mm joint, you get about 42 bricks per m². This is calculated as 1 m² divided by (0.225 m × 0.1125 m) = 39.5, but rounding up and accounting for the actual brick dimensions gives around 42. In the US with modular bricks, the figure is about 6.75 bricks per square foot, which is roughly 73 per m².

Do I need to add wastage to the brick count?

Yes, always add 5–10% for breakage, cutting, and future repairs. For a simple garden wall, 5% is usually enough; for a complex house with many openings and corners, use 10%. If you are ordering from a supplier, check if they allow returns – some do, which can reduce the need for over-ordering.

How do I account for a cavity wall?

A cavity wall has two leaves (inner and outer), each typically half a brick thick. So you calculate the bricks for one leaf (using the wall length and height) and then double the result. If the leaves are different sizes (e.g., a brick outer leaf and a block inner leaf), only double the brick leaf.

What if I use a different brick size?

Just change the brick length and depth in the calculator. The formula works for any rectangular brick. For example, if you use a 200 mm × 100 mm brick with a 10 mm joint, the bricks per m² becomes 1 / (0.210 × 0.110) = 43.3, so about 44 bricks per m².

Can I use this calculator for pavers or blocks?

Yes, the same area-based method works for any rectangular unit, including concrete blocks, pavers, and even tiles. Just enter the unit’s length and height (or width for pavers) and the joint thickness. For pavers laid without mortar, set the joint to 0 mm.

Why is my calculated count different from a builder’s estimate?

Builders often use a rule of thumb (e.g., 60 bricks per m² for a half-brick wall) that already includes wastage and assumes a specific brick size. The calculator gives a precise count for your exact dimensions, but the builder’s estimate may be higher to cover breakage and offcuts. It is always safer to round up.

Related

• Drywall Calculator by Wall: Sheets & Cost
• Drywall Calculator for Ceilings: Sheets & Waste
• Drywall Calculator Lowe’s: Estimate Sheets & Cost

in l | Wall length | m | 5 | 0
in h | Wall height | m | 2.4 | 0
in b | Brick length | mm | 215 | 0
in d | Brick depth | mm | 102.5 | 0
in j | Mortar joint | mm | 10 | 0
out bricks | Number of bricks | bricks | (ceil(l*1000/(b+j)) * ceil(h*1000/(d+j))) | 0
out area | Wall area | m² | l*h | 2
out mortar | Mortar volume | m³ | ((l*1000/(b+j))*(h*1000/(d+j)))*(b*d*j/1e9) | 3