Concrete Volume Calculator
Estimate the cubic metres of concrete required for slabs, footings, and walls. Enter your pour's length, width, and thickness to get the exact volume before ordering from a batch plant.
About this calculator
Concrete is ordered and priced by volume, so knowing exactly how many cubic metres you need prevents costly over-ordering or frustrating shortfalls. The formula is straightforward: Volume = length × width × thickness. All three dimensions must be in the same unit (metres) before multiplying. For example, a 100 mm slab must be entered as 0.1 m. The result gives you the net volume; most professionals add a 5–10% waste factor to account for spillage, uneven sub-base, and form blowouts. For irregular shapes, break the area into rectangles, calculate each volume separately, and sum the totals.
How to use
Suppose you are pouring a driveway slab 6 m long, 3 m wide, and 0.15 m thick (150 mm). Enter Length = 6, Width = 3, Thickness = 0.15. The calculator computes: Volume = 6 × 3 × 0.15 = 2.7 m³. Adding a 10% waste allowance: 2.7 × 1.10 = 2.97 m³. You would order 3 m³ from your ready-mix supplier. This simple check can save hundreds of dollars compared to guessing.
Frequently asked questions
How do I calculate concrete volume for a circular slab or column?
For a circular shape, use Volume = π × radius² × thickness. This calculator handles rectangular pours; for circles, compute the area (π × r²) first, then multiply by the thickness manually. For a column 0.3 m in diameter and 3 m tall, the volume is π × 0.15² × 3 ≈ 0.21 m³. Always add a waste factor of at least 5% for circular pours because formwork can flex slightly.
What waste factor should I add to my concrete volume calculation?
Industry practice is to add 5–10% for slabs on grade, 10% for walls and columns, and up to 15% for footings poured directly against earth. The extra material accounts for sub-base irregularities, formwork deflection, and unavoidable spillage. Ordering too little risks a cold joint if a second truck is delayed, which weakens the finished pour. It is always cheaper to return a partial load than to have a structural cold joint repaired.
Why does concrete volume need to be converted to tonnes for ordering?
Ready-mix plants often quote by volume (m³) but transport weight determines truck loads and road permits. Normal-weight concrete weighs approximately 2,400 kg/m³ (2.4 t/m³). A 5 m³ order weighs roughly 12 tonnes, which may require a full agitator truck. Knowing the weight also helps structural engineers verify that the supporting formwork and shoring are rated for the load before the pour begins.