Concrete Calculator
Calculate the volume of concrete you need for a slab, and how many bags of premixed concrete that requires.
How is it calculated?
Volume (m³) = length × width × thickness. Bags needed = volume ÷ yield per bag, rounded up. The yield (m³ a bag produces) is stated by the manufacturer on the packaging and varies by product — check the spec sheet before buying.
Examples
4 × 3 m slab, 10 cm thick, bags yielding 0.0125 m³
You need 1.2 m³ of concrete: 96 bags.
5 × 2 m slab, 15 cm thick, bags yielding 0.0125 m³
You need 1.5 m³ of concrete: 120 bags.
From the slab's volume to the bags
Volume is length × width × thickness in meters. A 4 × 3 m slab, 10 cm thick, needs 1.2 m³.
Bags work for small jobs; from about one or two cubic meters on, ordering ready-mix concrete usually pays off. Add a 5-10% margin for ground irregularities. Then calculate the binder with the cement calculator and the surface with square meters.
Premixed concrete bags versus a concrete plant
For small volumes (up to 1-2 m³) it's usually more practical to buy premixed concrete bags and mix them with water on site. For larger volumes, ordering concrete from a plant delivered by truck is usually cheaper per m³ and avoids mixing dozens of bags by hand — get quotes for both before deciding.