Concrete Calculator

Calculate concrete volume for slabs, footings and columns in m³ or yd³, plus the number of premix bags.

How much concrete do I need for a slab?

Volume = length × width × thickness. A 3 m × 3 m slab, 10 cm thick, needs 0.9 m³ (about 1.18 yd³), or 0.99 m³ with 10% extra for waste and uneven ground. The calculator converts this into the number of premix bags.

Bag yields

Bag	Yield
80 lb (36 kg)	0.60 ft³ (0.017 m³)
60 lb (27 kg)	0.45 ft³ (0.013 m³)
40 lb (18 kg)	0.30 ft³ (0.008 m³)

Typical thickness: 10 cm (4 in) for patios and paths, 15 cm (6 in) for driveways.

Frequently asked questions

How much extra should I order?

Add 5–10% for spillage and uneven sub-base.

When should I order ready-mix?

For more than about 1 m³ (1.3 yd³), a truck is usually cheaper and easier than bags.

Does it handle round columns?

Yes, choose “Round column” and enter the diameter and height.