Foundation Calculator South Africa
Work out how much concrete, cement and reinforcement your foundation needs before you order. Choose your foundation type, enter your dimensions, pick a concrete grade, and get an instant material breakdown for strip, pad, raft, slab and beam foundations.
Calculate My Foundation ↓Foundation Calculator
Select your foundation type, enter your dimensions, choose a concrete grade, then press Calculate.
Concrete Volume (with waste)
0 m³
Foundation summary
Material breakdown
| Material | Quantity | Notes |
|---|
This total adds waste allowance to your net concrete volume, then works out cement, sand and stone from your selected mix.
For a typical single-storey house strip foundation, 30m long at 600mm wide and 400mm deep, you need roughly 7.2 m³ of concrete before waste. At 25 MPa, that works out to about 55 bags of 50kg cement, plus sand and stone. SANS 10400-H sets a minimum trench depth of 400mm and a minimum foundation thickness of 200mm, but always confirm your exact depth against your soil report. Use the calculator above for a total based on your specific dimensions.
How to Use the Foundation Calculator
Four quick steps to an accurate material estimate for your foundation.
- 1 Choose your foundation type. Strip, pad, raft, beam on elastic foundation, or slab, depending on what your plans specify.
- 2 Enter your dimensions. Fields update automatically based on your foundation type. Use your approved building plans or your engineer’s specification.
- 3 Select your concrete grade and waste allowance. 25 MPa is the common default for house foundations, and a 10% waste allowance covers most sites.
- 4 Press Calculate. Your concrete volume, cement bags, sand, stone and a rough reinforcement estimate appear instantly. Use “Copy Result” to share it with your supplier.
The Foundation Concrete Formula
Concrete volume comes from your dimensions. Material quantities scale from that volume using your selected mix ratio.
Total Volume = Net Volume × (1 + Waste Allowance %)
Cement Bags = Total Volume × Bags per m³ for Selected Grade
Sand (m³) = Total Volume × Sand m³ per m³ for Selected Grade
Stone (m³) = Total Volume × Stone m³ per m³ for Selected Grade
Reinforcement (kg) = Net Volume × kg per m³ for Foundation Type (planning estimate only)
Concrete is priced and ordered by the cubic metre, so getting the net volume right, then adding a sensible waste allowance for spillage and over-excavation, is the single most useful number for budgeting a foundation pour.
Worked Examples
Real calculations using the mix quantities in this tool, so you can see exactly how the total is built.
Example 1: Strip foundation, 30m long, 600mm wide, 400mm deep, 25 MPa, 10% waste
| Net volume (30 × 0.6 × 0.4) | 7.20 m³ |
| With 10% waste | 7.92 m³ |
| Cement (7 bags/m³) | 55.4 bags |
| Sand (0.70 m³/m³) | 5.54 m³ |
| Stone (0.70 m³/m³) | 5.54 m³ |
Example 2: 6 pad foundations, 600 × 600 × 500mm each, 30 MPa, 5% waste
| Net volume (6 × 0.6 × 0.6 × 0.5) | 1.08 m³ |
| With 5% waste | 1.13 m³ |
| Cement (10 bags/m³) | 11.3 bags |
| Sand (0.65 m³/m³) | 0.74 m³ |
| Stone (0.65 m³/m³) | 0.74 m³ |
Example 3: Slab foundation, 10m × 8m, 150mm thick, 20 MPa, 10% waste
| Net volume (10 × 8 × 0.15) | 12.00 m³ |
| With 10% waste | 13.20 m³ |
| Cement (6.2 bags/m³) | 81.8 bags |
| Sand (0.72 m³/m³) | 9.50 m³ |
| Stone (0.72 m³/m³) | 9.50 m³ |
Foundation Concrete in South Africa: The Complete Guide
A house is only as good as what it stands on, and getting the concrete volume and mix right for your foundation avoids both under-ordering, which delays a pour, and over-ordering, which wastes money. South African foundation work is governed by SANS 10400-H, which sets minimum requirements that your local authority and engineer will check against your specific site and soil conditions.
What SANS 10400-H requires as a minimum
For a standard strip foundation trench, SANS 10400-H sets a minimum depth of 400mm below the original ground level, and a minimum average foundation thickness of 200mm. Basic, uncomplicated foundations should use concrete of at least 10 MPa, or a 1:4:5 cement:sand:stone mix by volume. These are minimums only, and problem soils such as heaving clay or dolomite typically require a geotechnical report and an engineer-designed foundation with greater depth and reinforcement.
Foundation types explained
- Strip foundation: A continuous concrete trench under load-bearing walls. The standard choice for most single and double-storey brick or block houses on reasonable soil.
- Pad foundation: An individual concrete block under a column or post, used where loads are carried by isolated points rather than continuous walls, such as steel-frame structures or carports.
- Raft foundation: A single reinforced concrete slab spanning the whole building footprint, often with a thickened edge beam. Used on weak or variable soil where a strip foundation would settle unevenly.
- Beam on elastic foundation: A structural beam designed against the supporting soil’s stiffness (soil modulus), used in engineered designs where load distribution along the beam matters more than a simple footing width.
- Slab foundation: A flat concrete slab used for ground-level floors, garages, and light structures without significant wall loads.
Concrete Mix Quantities per Cubic Metre
| Grade | Typical use | Cement (50kg bags) | Sand | Stone |
|---|---|---|---|---|
| 20 MPa | General use, light footings | 6.2 bags | 0.72 m³ | 0.72 m³ |
| 25 MPa | Standard house foundations | 7.0 bags | 0.70 m³ | 0.70 m³ |
| 30 MPa | Structural elements, beams, columns | 10.0 bags | 0.65 m³ | 0.65 m³ |
| 35 MPa | Heavy-duty, high-load applications | 11.5 bags | 0.60 m³ | 0.60 m³ |
The 25 MPa and 30 MPa figures come directly from the SANS 10400 / Cement and Concrete Institute batching tables. The 20 MPa and 35 MPa figures are interpolated from that same table for planning purposes, since they are not separately published, and can vary by supplier and stone size.
Do I need reinforcement in a foundation?
SANS 10400-H does not automatically require reinforcement in every foundation, but many architects include it as standard practice even where a soil report isn’t mandated, and it becomes necessary on problem soils or where a local authority requires it. This calculator’s reinforcement figure is a rough thumb-rule planning allowance, not a structural design, and actual bar size, spacing and cover must be specified by a qualified engineer.
Tips for ordering foundation materials
- Order concrete by the cubic metre, not by the bag, for large pours. Ready-mix suppliers price and deliver by m³, and it’s usually more cost-effective than bagged cement for anything over a few cubic metres.
- Always add a waste allowance. Trench over-excavation, spillage, and formwork losses are normal, not a sign something went wrong.
- Get a soil report on doubtful ground. Heaving clay, dolomite, or filled ground can turn a simple strip foundation into an engineered design overnight.
- Match your grade to your use. Using a higher grade than required wastes cement; using a lower grade than required risks structural failure.
- Keep your foundation trench dry before pouring. Standing water in the trench weakens the concrete-to-soil bond and can wash out cement paste.
Methodology
Concrete volumes are calculated directly from the dimensions you enter for each foundation type. Cement, sand and stone quantities are based on published SANS 10400 / Cement and Concrete Institute batching ratios for 25 MPa and 30 MPa, with 20 MPa and 35 MPa interpolated for planning purposes. Reinforcement estimates use common industry thumb-rules (40 kg/m³ for footings, 80 kg/m³ for slabs and rafts, 120 kg/m³ for beams) and are not a substitute for an engineer’s design.
Assumptions used in this calculator
- Concrete volume is calculated as length × width × depth for the selected foundation type, with a simplified thickened-edge allowance for raft foundations.
- Soil modulus for beam on elastic foundation is shown for reference only and does not affect the concrete volume calculated here.
- Reinforcement figures are rough thumb-rule planning allowances, not structural design quantities.
- Cement is assumed to be sold in standard 50kg bags.
Frequently Asked Questions
It depends on your foundation length, width and depth. For a typical 30m strip foundation at 600mm wide and 400mm deep, you need roughly 7.2 m³ before waste. Use the calculator above with your own dimensions for an exact figure.
SANS 10400-H sets a minimum strip foundation trench depth of 400mm below the original ground level, with a minimum average foundation thickness of 200mm. These are minimums only, and your local authority or engineer may require more depending on your soil.
It depends on your concrete grade. A 25 MPa mix, common for house foundations, needs about 7 bags of 50kg cement per m³. A 30 MPa mix needs about 10 bags per m³. Higher grades need more cement per cubic metre.
A strip foundation is a continuous concrete trench that runs under load-bearing walls, common in standard brick or block houses. A pad foundation is an individual concrete block supporting a single column or post, common in steel-frame structures, carports and pergolas.
Not always by default under SANS 10400-H, but many architects specify it as standard practice, and it becomes necessary on problem soils such as heaving clay or dolomite. Your engineer or the plans approved by your local authority will confirm what’s required for your site.
A 10% waste allowance covers normal spillage, over-excavation, and uneven trench walls for most residential sites. Well-formed, precisely dug trenches can use as little as 5%, while rough or hand-dug trenches on uneven ground may need 15%.
For small jobs like a few pad foundations, site-mixed bagged cement is often practical. For larger pours, typically above 3 to 5 m³, ready-mix delivered by a concrete supplier is usually more cost-effective and gives more consistent strength across the whole pour.
25 MPa is the common default for reinforced house foundations in South Africa. Lighter, unreinforced work can use 20 MPa or the SANS 10400 minimum of 10 MPa, while structural elements like columns and beams often specify 30 MPa or higher. Always follow your approved plans or engineer’s specification.