Concrete Calculator

Calculate how much concrete (m³ or bags) you need for any slab, footing or column.

✓ Free to use ✓ Instant results ✓ Mobile friendly ✓ No sign-up needed

Shape

Length (m)

Width (m)

Depth / Thickness (m)

Volume (m³)

25kg Bags Needed

With 10% Waste

🏗️ Get the right tools for the job

Concrete Volume Formula

Volume = Length × Width × Depth (all in metres). Add 10% for waste. One 25kg bag covers roughly 0.012 m³.

How many bags of concrete do I need for a 3m × 3m slab?+

At 100mm depth: 0.9 m³. This requires approximately 75 × 25kg bags, plus 10% waste = ~83 bags.

What concrete mix ratio should I use?+

For general slabs: 1:2:4 (cement:sand:aggregate). For structural work: 1:1.5:3.