Calculate how many cubic meters and bags of ready-mix concrete you need for a foundation, slab or footing, based on length, width and thickness.
The volume is simply length × width × thickness, once the thickness is converted from centimeters to meters:
A 25 kg bag of ready-mix concrete yields roughly 12.5 liters (0.0125 m³) of poured concrete. Divide the volume by this number, rounded up, to find the bag count. Weight is calculated using a typical density of 2,400 kg per cubic meter.
It depends on what will stand on it. A deck footing often works with 8–10 cm, while a load-bearing garage or house foundation typically needs 10–15 cm or more, and should be assessed by a professional.
For smaller amounts (under about 1–1.5 m³), bags from a building supply store are most practical. For larger pours, it's often worth ordering ready-mix concrete delivered by truck.
Most foundations and slabs should be reinforced with mesh or steel to prevent cracking and increase load-bearing capacity. This calculator only computes concrete volume, not reinforcement needs.