How a brick foundation is estimated
A brick foundation calculator works out how many bricks fill the volume of a masonry footing, allowing for the mortar joint around each brick, then estimates the cement and sand for that mortar. You enter the foundation's length, width and depth, the number of layers, a brick size, the joint thickness, a wastage percentage and, optionally, a cement:sand ratio.
The formulas
- Foundation volume = Length × Width × Depth × Number of layers
- Brick with mortar = (Brick length + joint) × (Brick width + joint) × (Brick height + joint)
- Bricks required = Length × Depth × Layers × (Width + joint) ÷ Brick-with-mortar volume, rounded up
- Total bricks = Bricks required × (1 + wastage %), rounded up
- Mortar volume = Foundation volume − (unrounded brick count × one brick's solid volume)
- Dry mortar volume = Mortar volume × 1.33
- Cement and sand = Dry volume split by the ratio, for example 1 part cement in 7 for 1:6
- Cement bags = Cement volume × 1,440 kg/m³ ÷ 50 kg per bag
One joint is added to the width because brickwork n bricks wide has only n − 1 mortar joints across it. With that joint added, (Width + joint) ÷ (Brick width + joint) is the number of bricks across the foundation.
The defaults are a modular brick, a 10 mm joint, 5% wastage and no mortar estimate. The 1.33 dry-volume factor, 1,440 kg/m³ cement density and 50 kg bag are the calculator's built-in conventions.
Brick sizes
| Preset | Brick size (mm) | Size with 10 mm joint (mm) | Bricks per m³, 600 mm wide (before wastage) |
|---|---|---|---|
| Modular | 190 × 90 × 90 | 200 × 100 × 100 | about 508 |
| Standard/Classic | 230 × 110 × 75 | 240 × 120 × 85 | about 415 |
| Custom | your dimensions | your dimensions + joint | depends on size |
Check the actual size of the bricks your supplier sells. Brick sizes differ between countries and manufacturers, and a few millimeters change the count noticeably over a whole foundation.
Worked example
A strip foundation 20 m long, 0.6 m wide and 0.3 m deep, one layer, modular bricks, 10 mm joints, 5% wastage, and 1:6 mortar:
- Foundation volume: 20 × 0.6 × 0.3 × 1 = 3.600 m³.
- Brick with mortar: 0.2 × 0.1 × 0.1 = 0.002 m³.
- Bricks required: 20 × 0.3 × 1 × (0.6 + 0.01) ÷ 0.002 = 1,830.
- With 5% wastage: 1,830 × 1.05 = 1,921.5, rounded up to 1,922 bricks.
- Solid brick volume: 0.19 × 0.09 × 0.09 = 0.001539 m³, × 1,830 = 2.816 m³. Mortar: 3.6 − 2.816 = 0.784 m³.
- Dry volume: 0.784 × 1.33 = 1.042 m³.
- Cement: 1.042 × 1/7 = 0.149 m³, × 1,440 ÷ 50 = 4.29 bags. Sand: 1.042 × 6/7 = 0.893 m³.
The same foundation with standard 230 × 110 × 75 mm bricks needs 1,496 bricks (1,571 with wastage), 0.763 m³ of mortar, 4.18 bags of cement and 0.870 m³ of sand.
Steps to use it
- Measure the foundation length along its centerline. At corners, avoid counting the overlap twice.
- Enter the width and depth of the brickwork, not of the trench or the concrete bed beneath it.
- Leave layers at 1 unless several layers really are the same size.
- Pick the brick size and joint thickness you'll build with.
- Choose a mortar ratio if you want cement and sand quantities.
Limitations
- Same-size layers. Real stepped footings get narrower as they rise. Estimate each step separately, as described in the FAQ.
- Concrete bed not included. Most brick foundations sit on a concrete base, which you can estimate with the concrete calculator.
- No wastage on mortar. Only the brick count gets the wastage allowance.
- Solid bricks assumed. Frogged or perforated bricks take more mortar than this estimate.
The calculator gives material quantities only. Foundation width, depth and construction must follow your local building code, and a qualified engineer should check the design for your soil and loads.
Related calculators
- Excavation calculator: volume of the trench you'll dig for the foundation.
- Brick calculator: bricks and mortar for the walls above ground.
- Block calculator: if you're using concrete blocks instead of bricks.
- Construction materials converter: convert cement bags and material volumes to weights.
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