Whether you're pouring a slab, path or footing, ordering the right amount of concrete matters — a short load can ruin a pour. This calculator gives you the volume and a bag estimate from three simple measurements.
Volume is length × width × thickness
The maths is basic multiplication, but the units trip people up: thickness is usually quoted in centimetres or inches while the area is in metres or feet. Everything must be in the same unit before multiplying — this calculator converts for you and returns the result in cubic metres or cubic yards.
Bags vs ready-mix
For small jobs, pre-mixed bags are convenient. But bags add up fast: a single cubic metre can need 80 or more 25 kg bags. Once you're past about a cubic metre, ordering ready-mix delivered by truck is usually cheaper, faster and gives a more consistent pour.
Frequently asked questions
Multiply length × width × thickness, keeping all three in the same unit. For a slab 4 m × 3 m × 0.1 m that's 1.2 m³. This calculator handles the unit conversions and adds a waste margin.
Divide the total volume by the yield per bag — roughly 0.0125 m³ for a 25 kg bag or 0.017 m³ (0.6 ft³) for an 80 lb bag. For larger pours, ready-mix is usually more economical.
About 5–10%. You can't top up a pour once it starts setting, and slight variations in sub-base level or slab thickness increase the real volume.