Structure
Estimate the volume of concrete for a rectangular slab with a uniform thickness. Enter the dimensions from your project specification and add a chosen allowance. This tool calculates quantity; it does not select the slab thickness, concrete strength or reinforcement for a project.
Your estimate
Concrete volume = length × width × depth × (1 + waste ÷ 100).
This estimates volume only. It does not design slab thickness, reinforcement, foundations or concrete strength. Confirm order increments with your supplier.
Currency labels do not convert prices. Enter all prices in the chosen currency.
Multiply slab length, width and depth, then add the ordering allowance. Check the depth unit carefully. This calculator estimates volume; it does not select slab thickness, reinforcement or concrete strength.
A 6 m by 4 m slab with a depth of 100 mm has a net volume of 2.4 m³. Adding a 5% allowance gives an order estimate of 2.52 m³.
Base volume = length × width × thickness. All three dimensions must use consistent units before multiplication. For metric inputs, a thickness of 100 mm becomes 0.1 m. A 100 mm slab is not calculated by multiplying its square metres directly by 100.
The ordering estimate multiplies the base volume by (1 + allowance percentage ÷ 100). The displayed cubic-yard result is a volume conversion. One cubic yard equals 0.764554857984 cubic metres; ordinary length or area conversion factors do not apply to volume.
A single rectangular calculation assumes a flat base and constant depth. Break a more complex shape into separate non-overlapping sections, calculate each volume and add the results. Thickened edges, steps and footings require their own quantities rather than being hidden inside the slab area.
Uneven excavation can change the required volume. Record depth measurements and discuss the allowance with the concrete supplier or installer. A chosen percentage is an estimate, not a guarantee that every variation in the base has been captured.
For ready-mixed concrete, compare the calculated volume with the supplier’s order increments and delivery arrangements. For bagged concrete, divide required volume by the mixed yield printed for that exact product and bag size, then round upward to complete bags.
QUIKRETE notes that its published calculator yields are approximate and exclude factors such as uneven substrate and waste. Dry bag weight alone is not a universal conversion to finished concrete volume. Cement, aggregate and premixed concrete are also different products and should not share an assumed yield.
Worked example
At a specified thickness of 100 mm, the base volume is 4 × 3 × 0.1 = 1.2 m³. A chosen 5% allowance gives 1.26 m³, approximately 1.65 yd³. If a selected bag produces 0.012 m³ of mixed concrete, this planning volume would require 105 bags.
No. Enter the thickness required by your project design. Suitability depends on the intended use, ground conditions and other project-specific requirements.
No. The result is finished concrete volume. Use a specified mix or the manufacturer’s bag yield to plan individual material quantities.
Manufacturer and measurement references for the assumptions described above.