Concrete Calculator
Calculate concrete volume, weight and number of cement bags for a slab.
Last updated: August 2026
Volume
2.25 m³
In cubic feet
79.5 ft³
Weight
5,400 kg
50 kg bags
108
Assumes standard concrete density of 2,400 kg/m³. Add 5–10% extra for spillage and uneven ground.
How it works
Volume = L × W × D. Weight = volume × 2,400 kg/m³. Bags = weight ÷ bag size.
Example: 5 × 3 × 0.15 m = 2.25 m³ ≈ 5,400 kg ≈ 108 bags of 50 kg.
Frequently Asked Questions
How much concrete do I need for a slab?
Multiply length × width × thickness. A 5 m × 3 m × 0.15 m slab is 2.25 m³, weighing about 5.4 tonnes — roughly 108 bags of 50 kg cement mix.
How many cement bags are in 1 cubic metre?
Assuming 2,400 kg per m³ of mixed concrete and 50 kg bags, one cubic metre needs about 48 bags of dry mix.
How much extra concrete should I order?
Add 5–10% for spillage, uneven subgrade and formwork inaccuracies. For a 2.25 m³ slab, order about 2.4 m³.
How thick should a concrete slab be?
Garden paths around 10 cm, patios and sheds 10–15 cm, and driveways 15–20 cm with reinforcement. Thinner slabs crack under vehicle loads.