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 volume is expressed in cubic metres. Supplier rounding occurs only when you enter the quote's cubic-metre increment.
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 concrete is ordered by the cubic metre. Small-load services may use different vehicles and commercial terms; confirm access, physical minimum, billed minimum and cartage.
- 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. A 10% example allowance gives 0.37 m³; the actual ready-mix order depends on the supplier's entered increment and minimum, while bagged supply depends on the exact product yield.
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 supplier may offer a smaller delivery vehicle for access or low-volume work, but capacity and pricing are not universal. Compare the complete quoted unit price, minimum, cartage and access terms with bagged-product yield and handling.
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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:
- 2026-07-23
- Formula version:
- 1.1.0
- 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 chosen allowance is applied to the exact volume. Supplier rounding occurs only when you enter the increment shown on the current quote; if that field is blank, the planning volume remains unrounded.
- The preliminary material cost multiplies the planning or supplier-rounded quantity by the price you enter. Tax is added only after you confirm that the entered price excludes tax and supply a rate; an unresolved basis produces a subtotal, not a final total.
- 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.
- Supplier order terms: Enter the exact cubic-metre increment and GST basis from the current supplier quote; neither is assumed.
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.