Calculate your result
Quick answer
A 5 m × 4 m slab at an illustrative 100 mm depth contains 2 m³. A 5% ordering allowance gives 2.1 m³, or 2,100 litres. Depth and allowance are example inputs, not a structural specification.
How it works
Use this concrete calculator for South Africa to estimate cubic metres, litres or cubic yards for slabs, foundations and post holes. Add separate sections and choose a ready-mix, bag or confirmed batch-recipe result.
Formula
Rectangular volume = length × width × depth, converted to metres. Add sections and extras, subtract volume deductions, apply allowance, then round up only to an entered supplier increment.
Assumptions and common mistakes
Check units, input values and the method before relying on an estimate. Review the existing tool notes and official sources below.
Formula
Rectangular volume = length × width × depth, converted to metres. Add sections and extras, subtract volume deductions, apply allowance, then round up only to an entered supplier increment.
How to use the concrete calculator South Africa
Choose a section shape and enter its count, dimensions and units. Add different sections instead of repeating a count for unequal shapes. Enter additional concrete only when it is not already in those sections. Deduct any known displaced volume, select an allowance and confirm any supplier order increment before calculating.
How much concrete do I need?
For a rectangle, multiply length, width and depth in metres. If you know an area in square metres, select Known area and multiply it by depth in metres. Round sections use pi × diameter² ÷ 4 × depth. The breakdown separates measured volume, deductions, allowance and order rounding so you can check each step.
Ready-mix concrete calculator
Choose the ready-mix result for a volume order, optional entered load capacity and your own quote. The load count is a minimum capacity calculation, not a dispatch plan. Confirm the required specification, supplier minimum, delivery access, pumping and any charges separately. No live South African concrete prices are assumed.
Concrete mix quantities from a confirmed recipe
The recipe option scales the cement mass, sand volume and stone volume of a batch with a known finished yield. All recipe quantities must come from your chosen specification or confirmed supplier instructions. A nominal ratio alone does not establish finished yield, water demand or achieved MPa. This tool does not design a mix.
Bags, fence posts and cubic yards
For complete concrete premix bags, enter the finished yield printed on the actual product. For holes, choose the matching round or rectangular post geometry and enter the embedded concrete depth. The result includes cubic yards using the international yard conversion; South African orders commonly use m³.
Concrete blocks and the calculator app question
Concrete blocks are masonry units, not a volume of wet concrete. Use the block brick calculator for their count. This tool runs in a phone or desktop browser without installing an app or registering as a visitor. It does not promise offline availability. Copy result includes your displayed measurements if you choose to share them.
Before ordering
The result estimates quantity only. Have concrete strength, reinforcement, ground preparation, slab or footing dimensions, placement and curing requirements confirmed for the actual job. Recheck measurements instead of using a waste percentage to conceal an uncertain excavation.
Area, depth and concrete volume examples
| Illustrative area | Illustrative depth | Measured volume, no allowance |
|---|---|---|
| 20 m² | 75 mm | 1.5 m³ |
| 20 m² | 100 mm | 2 m³ |
| 20 m² | 150 mm | 3 m³ |
| 35 m² | 120 mm | 4.2 m³ |
These are arithmetic examples without allowance. The example depths are not design recommendations.
Last reviewed: 15 October 2026. Reviewed by the 99tools team. Editorial and corrections policy.
Quantity planning only. Confirm product suitability, concrete specification, reinforcement and site requirements for the actual project.
Related construction calculators
- Concrete Slab Calculator South Africa
- Foundation Calculator South Africa
- Premix Concrete Calculator South Africa
- Concrete Bags Calculator South Africa
- Cubic Metre Calculator South Africa
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Concrete guides
- How to Calculate Concrete Volume in South Africa
- How Many Concrete Premix Bags Do I Need?
- Concrete Mix Quantities: Cement, Sand and Stone
- Ready-Mix Concrete Order Guide South Africa
- How Much Concrete for Fence Posts?
- Slab Diagonal and Sub-Base Quantity Checks
- Compare Concrete Calculators: PPC, AfriSam and BUCO
- Foundation Quantities: Strip, Pad and Raft
- How to Calculate Foundation Cost in South Africa
- How to Square a Building Foundation
- Concrete Slab Cost in South Africa
- Solid, Precast and Reinforced Concrete Slabs
- Concrete Slab Curing, Drying and Repairs
- 40 kg Premix Concrete: Yield and Coverage
- Premix Concrete Prices and Product Checks
- Cubic Metres, Litres and Area Conversions
- Cubic Metres to Tonnes and Wheelbarrows
- Concrete Bags per m³ and Fence Post Volumes
Frequently asked questions
How much concrete do I need for a slab?
Multiply length × width × depth in metres, then add only an agreed ordering allowance. For 5 × 4 × 0.1 m the measured volume is 2 m³.
Can I convert square metres to cubic metres?
Yes, but a depth is required. Area in m² × depth in metres gives m³.
Does this calculate sand and gravel?
The confirmed batch-recipe option scales sand and stone quantities from your entered recipe and finished yield. It does not invent a mix strength.
Can I calculate concrete around a fence post?
Yes. Select a post-hole shape and enter both the hole and embedded post dimensions, count and concrete depth.
Does it calculate how many concrete blocks I need?
Use the separate block brick calculator for installed block quantities. Wet concrete volume and masonry unit count are different calculations.
Are my measurements stored online?
No calculator measurements are sent to the website database. They remain in the browser unless you choose to copy, print or share them.
Related calculators
Foundation Calculator South Africa
Calculate foundation concrete in South Africa from measured strips, pads or raft sections. Add your quoted costs and check a rectangular set-out diagonal.
Block Brick Calculator South Africa
Use this block brick calculator for South Africa to estimate masonry units from measured walls and openings. Compare actual unit coverage and full-pack.
Concrete Slab Calculator South Africa
Calculate slab concrete volume, premix bags or quoted costs from rectangles, triangles, circles or known area. Check sub-base volume and rectangle diagonals.
Premix Concrete Calculator South Africa
Calculate premix concrete bags from project dimensions and confirmed finished yield. Check packs, coverage at your depth and material costs from your quote.
Helpful guides
How to Calculate Concrete Volume in South Africa
Calculate concrete volume by converting every dimension to metres and multiplying length × width × depth. Keep measured volume separate from allowance and.
Sand and Cement Mix Ratios: Mortar, Plaster and Screed
Understand cement:sand ratios, volume batching and the difference between bricklaying mortar, plaster, screed, concrete and complete premix.
How Much Sand and Cement per m² or 1,000 Bricks?
Convert plaster thickness or a confirmed brickwork mortar yield into cement bags and sand without assuming one quantity for every wall.