Concrete & Masonry
Concrete Volume Calculator
Enter your pour dimensions in metres and millimetres — rectangular slabs and footings or cylindrical post holes — to get the cubic metres of pre-mixed concrete to order, with wastage and an optional GST-aware cost estimate.
Formula tested · Local units · No sign-up
Project inputs
Enter measurements
Use your preferred units. Results update automatically.
Show the calculation methodFormula, conversions, rounding, and assumptions+
Rectangular pours use volume = length × width × depth; cylindrical pours (fence and pergola post holes, bored piers) use volume = π × (diameter ÷ 2)² × depth, multiplied by the number of pours.
Australian practice measures plan dimensions in metres and depth in millimetres, so the calculator converts before multiplying — 100 mm is 0.1 m.
Pre-mixed concrete is sold by the cubic metre and the result is rounded up to the next quarter cubic metre.
Real-world example
Worked example: 6 m × 4 m carport slab, 100 mm thick
- Convert depth: 100 mm = 0.1 m.
- Volume: 6 × 4 × 0.1 = 2.4 m³.
- Add 10% wastage: 2.4 × 1.10 = 2.64 m³.
- Round up to the ordering increment: 2.75 m³.
Order 2.75 m³. Enter your local quote per m³ — advertised consumer prices in Australia normally include 10% GST.
Before you start
How to measure
- Measure formwork length and width in metres and depth in millimetres from the compacted base to finished level, using the deepest reading.
- For post holes, measure the auger or hole diameter in millimetres and the depth, then use the cylindrical shape with the number of holes.
- Split L-shaped or stepped pours into rectangles and run them as separate calculations, or add the volumes.
Local guidance
Notes for Australia
- Pre-mixed (pre-mix) concrete is ordered by the cubic metre; mini-mix trucks handle small loads where a full agitator can't get access.
- Structural slabs and footings on Australia's widespread reactive clay soils are engineering matters under Australian standards — this tool estimates volume only.
- GST is 10% and consumer prices are usually advertised GST-inclusive; trade accounts often see ex-GST pricing.
Quick reference
Volume formulas by pour shape
| Shape | Formula | Typical use |
|---|---|---|
| Rectangular | length × width × depth | Slabs, footings, paths |
| Cylindrical | π × (diameter ÷ 2)² × depth | Post holes, bored piers |
Planning formulas only — augered holes in reactive clay often end up oversize, so allow wastage.
Good to know
Common mistakes to avoid
- Typing depth in centimetres into a millimetre field — 10 instead of 100 gives one-tenth of the required volume.
- Using the full diameter instead of the radius when checking post-hole volume by hand.
- Comparing GST-inclusive and ex-GST quotes as if they were the same.
- Pouring structural footings on reactive clay without engineering advice.
Need help?
Frequently asked questions
How much concrete for 8 pergola post holes, 300 mm diameter and 600 mm deep?
Each hole is π × 0.15² × 0.6 = 0.042 m³, so eight holes are 0.34 m³. With 10% wastage that's 0.37 m³ — order 0.5 m³ from a mini-mix, or use rapid-set post-mix bags.
How much for a 3 m × 2 m path at 75 mm?
3 × 2 × 0.075 = 0.45 m³ exactly. With 10% wastage that's 0.495 m³, so order 0.5 m³.
What's a mini-mix truck and when do I need one?
A smaller agitator that delivers small loads (often 0.5–2 m³) into tight access, usually at a higher per-metre rate than a full truck. For most post-hole and small-path jobs it beats hand-mixing dozens of bags.
Keep planning
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About this calculator
- Written by:
- BuildMeasure Editorial Team
- Technically reviewed by:
- Pending independent technical reviewer (formula unit-tested; see methodology)
- Last reviewed:
- 2026-07-16
- Formula version:
- 1.0.0
- Region reviewed for:
- Australia
- Spotted an error?
- Report a correction
Methodology
- Rectangular pours use volume = length × width × depth × count; cylindrical pours use volume = π × (diameter ÷ 2)² × depth × count. All inputs are converted to SI units (metres) before any arithmetic to avoid unit drift.
- The wastage allowance is applied to the exact volume, then the total is rounded UP to the next 0.25 of the regional ordering unit (cubic yards in the US, cubic metres elsewhere), because ready-mix suppliers typically sell in quarter-unit increments.
- The cost estimate simply multiplies the suggested order quantity by the price you enter, then applies the tax rate you enter. No prices are built in.
- The formula is covered by automated unit tests, including hand-calculated worked examples, and is versioned (see formula version on this page).
Sources & standards
- Unit definitions: Metric units throughout; 1 m³ = 1,000 litres.
- Ordering increments: Quarter-cubic-metre increments are typical for pre-mixed concrete; confirm with your supplier.
This tool provides a material estimate for planning purposes only. It is not a quotation, and it does not size reinforcement, check ground conditions, or replace professional structural advice. Confirm quantities and mix specification with your supplier before ordering.