Concrete Volume Calculator, South Africa
Calculate m³ of concrete for slabs, foundations, columns and driveways. Includes cement, sand and stone quantities for SA mix ratios.
Quick answer: Concrete volume is calculated as Length × Width × Depth in metres, giving a result in cubic metres. A driveway slab of 6m × 3m × 0.1m (100mm thick) needs 1.8m³ of concrete. Add 10% as a standard allowance for wastage and spillage. Ready-mix concrete is ordered by the cubic metre in South Africa.
Concrete Calculator
Enter Element Details
For planning purposes only. Consult a structural engineer or contractor before pouring structural concrete.
How to Use This Calculator
- Select element typeChoose slab or driveway, strip foundation, column or pier, or pad foundation. The input fields below update to match your choice.
- Enter lengthEnter the length in metres. For a slab or driveway this is the longest dimension; the field label adjusts for other element types.
- Enter widthEnter the width in metres. For a slab or driveway this is the shortest dimension; the field label adjusts for other element types.
- Enter thickness or depthEnter the thickness or depth in millimetres. 100mm is the standard residential slab thickness.
- Enter quantityEnter the number of identical elements. Use this for multiple columns or pad foundations.
- Select mix typeChoose 1:2:3 for structural elements, 1:4:4 for general slabs and driveways, 1:3:6 for blinding or non-structural fill, or ready-mix 20MPa if ordering from a batching plant.
- Select wastage factorChoose 10% as standard, 15% for uneven ground or complex formwork, or 5% for a simple flat slab.
- Click CalculateResults show total concrete volume in cubic metres including wastage, cement bags, sand and stone volumes for site mixing, and a ready-mix quantity and cost estimate, plus the area the pour covers in square metres.
Concrete Calculations in South Africa: Complete Guide
Concrete is the most fundamental building material in South African construction, used for foundations, slabs, driveways, columns, paths and pools. Getting the volume calculation right before you order is critical. Too little means a cold joint (a structural weakness) if you have to stop and wait for more, and over-ordering is expensive waste. Once you have the quantity, the Building Cost Calculator shows where concrete sits in the cost of the whole build, and How to Budget for Building a House in SA explains how to plan that budget.
SA Concrete Mix Ratios Explained
| Mix Ratio | Cement:Sand:Stone | Strength (approx) | Best Use |
|---|---|---|---|
| 1:2:3 | 1 bag : 2 parts : 3 parts | ~25 MPa | Foundations, columns, beams, structural slabs |
| 1:4:4 | 1 bag : 4 parts : 4 parts | ~20 MPa | Driveways, pathways, general floor slabs |
| 1:3:6 | 1 bag : 3 parts : 6 parts | ~15 MPa | Blinding layers, mass fill, non-structural |
| 20 MPa ready-mix | Factory batched | 20 MPa | Residential slabs, driveways, general use |
| 25 MPa ready-mix | Factory batched | 25 MPa | Structural elements, engineer-specified |
Concrete Volume Formula
Volume (m³) = Length (m) × Width (m) × Depth (m) × Quantity
Order quantity = Net volume × Wastage factor (1.05 to 1.15)
Cement bags (1:2:3) = Volume × 6.8 bags per m³
Sand (m³) = Volume × 0.50 (1:2:3 mix)
Stone (m³) = Volume × 0.75 (1:2:3 mix)
Slab Thickness Guide for SA Conditions
- Pathways (pedestrian only): 75–100mm minimum, no reinforcement needed for short spans
- Residential driveway (passenger cars): 100mm minimum with BRC mesh reinforcement
- Driveway (bakkies/heavy vehicles): 150mm with BRC mesh and compacted sub-base
- House floor slab: 100–125mm with BRC mesh on compacted fill
- Strip foundation: 200mm deep minimum, engineer to specify based on soil
- Sub-base under any slab: 100mm compacted G5 or crusher run
Ready-Mix vs Site-Mixed Concrete in South Africa
Ready-mix concrete (ordered from a batching plant and delivered by truck mixer) is the usual choice for larger volumes in South Africa. It is more consistent, higher quality and often more cost-effective once you account for the labour to mix on site. Ready-mix is priced per m³. Our estimate from published list prices in October 2026 puts 20MPa at about R1,100 to R1,800/m³ delivered, VAT included, so get a quote from your nearest plant. Some suppliers deliver from 1m³, but a part-load charge usually applies to small orders: AfriSam, for example, charges one on any load under 5m³, and its trucks carry 6m³ or 8m³. Ask your supplier for its threshold and rate.
For small volumes under 1m³, mixing on-site with a drum mixer is practical. Use a consistent scoop measure for cement, sand and stone. Never estimate by eye, as inconsistent mixes produce weak concrete.
Reinforcement and Curing in SA Conditions
Plain concrete is strong in compression but weak in tension. Any slab subject to vehicle loads or spanning a variable sub-base must be reinforced. BRC welded mesh, typically Ref 193 for light residential slabs or the type your engineer or mesh supplier specifies, is the usual choice for residential driveways and floor slabs, placed at mid-depth on bar chairs. Expansion joints are essential in slabs longer than 4–6 metres. Saw-cut control joints to one-quarter the slab depth within 24 hours of placing to prevent random shrinkage cracking.
Curing is critical in South Africa's hot, dry climate. Cover fresh concrete with wet hessian or plastic sheeting immediately after finishing and keep it moist for at least 7 days, which is common site practice. In hot weather avoid pouring in direct midday sun without shading. SANS 10100-2 sets a permissible maximum of 35°C for the fresh concrete, so keep the fresh concrete below that limit: cool the materials, pour early or late in the day and ask your supplier about retarders. Concrete that gets too hot loses workability too fast and produces a weak, dusty surface.
A Worked Example: Concrete for a Double Carport Slab
Consider a double carport slab measuring 6m × 5.5m at the standard residential slab thickness of 100mm (0.1m). The raw volume is 6 × 5.5 × 0.1 = 3.3m³ over a 33m² footprint (the calculator's Area Covered result). Adding the standard 10% wastage allowance for spillage, over-excavation and uneven sub-base brings the order quantity to approximately 3.63m³. Most suppliers will round this up to 3.75m³ or the nearest quarter-cubic-metre increment their mixer truck can deliver. At a typical 20MPa mix (suitable for driveways and carports under normal vehicle loads), this slab also needs reinforcement mesh (typically Ref 193 for a residential carport, or the type your engineer or supplier specifies) and moist curing for at least 7 days (common site practice) before the surface bears vehicle weight; full design strength is reached at 28 days. Ready-mix is usually worthwhile for larger pours because it gives more consistent strength across the full pour than hand-mixed batches, although a part-load charge on small loads (AfriSam charges one under 5m³, so this 3.63m³ slab could attract it) can erode the saving over site-mixing. Site-mixed concrete becomes more attractive for very small pours, such as a single post base or small repair, where a part-load charge would otherwise mean paying for far more concrete than the job actually requires. Whichever route is chosen, asking a ready-mix supplier to confirm the mix is made to SANS 878 and to state its strength grade, or using the correct volumetric ratios for site-mixed concrete, helps ensure the finished slab reaches its intended design strength rather than an unverified approximation of it.
Planning the whole build, not just the concrete? See the Developer's Build Cost Planning Guide →
Frequently Asked Questions
Concrete volume is calculated as Length × Width × Depth in metres, giving a result in cubic metres (m³). For a driveway slab of 6m × 3m × 0.1m (100mm thick), you need 1.8m³ of concrete. Add 10% as a standard allowance for wastage and spillage. Ready-mix concrete is ordered in m³. Some suppliers deliver from 1m³, but small loads usually carry a part-load charge (AfriSam charges one below 5m³), so ask your supplier.
The most common concrete mix ratios used in South Africa are: 1:2:3 (1 cement : 2 sand : 3 stone) for structural concrete such as foundations, columns and beams; 1:3:6 for blinding, mass fills and non-structural applications; and 1:4:4 for general driveways and slabs. Ready-mix concrete is specified by strength grade. 20MPa is standard for residential slabs and foundations.
For a 1:2:3 mix, approximately 6–7 bags of 50kg cement are needed per m³ of concrete. For a weaker 1:3:6 mix, approximately 4 bags per m³ are needed. These figures account for the fact that aggregate fills some of the void, so you need less cement volume than the dry mix suggests. Ready-mix suppliers calibrate this precisely.
For a residential driveway carrying standard passenger vehicles, a minimum slab thickness of 100mm (10cm) is common practice in South Africa. For heavier vehicles such as bakkies, trucks or heavy SUVs, increase to 150mm. Slabs should be reinforced with BRC mesh (typically Ref 193, or the type your engineer or supplier specifies) and have a compacted sub-base of at least 100mm of G5 or crusher run material.
For very small pours, mixing on-site with a mixer is cost-effective. For larger volumes, ready-mix concrete from a batching plant is usually more economical (allowing for any part-load charge on small loads) and produces a more consistent, quality-controlled product. Ready-mix 20MPa costs roughly R1,100 to R1,800 per m³ according to published list prices (October 2026, our estimate), depending on province and supplier; higher grades cost more. The labour saving alone often justifies ready-mix for larger pours.
A typical strip foundation for a 3-bedroom house is approximately 400mm wide × 200mm deep (or deeper depending on soil conditions). For a house with a 50m perimeter, this gives roughly 50m × 0.4m × 0.2m = 4m³ of concrete just for the strip. A structural engineer should specify foundation depth and width based on actual soil bearing capacity.
Ready-mix concrete costs roughly R1,000 to R2,100 per m³ according to published list prices in October 2026 (our estimate), depending on strength (15MPa to 35MPa), region and delivery distance. 20MPa, the standard grade for residential slabs and foundations, sits towards the lower end of that band, typically R1,100 to R1,800/m³ delivered with VAT included. Small loads can attract a part-load charge on top of the per-m³ rate, so ask your supplier.
A 1:2:3 mix (1 cement : 2 sand : 3 stone) is standard for residential strip footings and raft foundations in South Africa. This produces approximately 25MPa strength. For suspended slabs or high-load applications, use 25–30MPa ready-mix from a certified batch plant.
Yes. Driveways and floor slabs are normally reinforced with BRC mesh (typically Ref 193, or the type your engineer or supplier specifies) to control cracking. The mesh is placed at mid-slab depth on bar chairs. Structural slabs carrying loads (suspended slabs, garage slabs, pool surrounds) should be designed by a structural engineer.