Concrete Calculator

Calculate cement bags, sand, and aggregate for slabs, columns & footings

Length (m)

Width (m)

Thickness (mm)

Typical floor slab: 100–150mm · Roof slab: 125–150mm

Concrete mix ratio

Wastage factor (%)

Concrete volume needed

—

🏗️

Cement bags (50kg)

—

🪨

Sand (fine aggregate)

—

m³ / kg

🪶

Aggregate (coarse)

—

m³ / kg

💧

Water (approx.)

—

litres

⚠️ Add 5–10% extra for wastage, spills, and formwork losses. These are dry material quantities. Wet concrete volume will be approximately 35–40% less than dry volume. Always consult a structural engineer for load-bearing elements.

Concrete Mix Ratios

What do the mix ratios mean?

The ratio 1:1.5:3 means 1 part cement : 1.5 parts sand : 3 parts aggregate by volume. M20 (1:1.5:3) gives 20 N/mm² characteristic compressive strength and is the standard mix for residential slabs and beams.

How many cement bags per cubic metre?

For M20 mix, approximately 6.4 bags (50kg each) per cubic metre of concrete. For M25, about 8 bags per m³. These are dry material quantities before mixing — wet concrete volume is less due to compaction.

What is dry volume factor?

When you mix dry ingredients, their combined volume shrinks when water is added and the mix compacts. The dry volume of ingredients needed is approximately 1.54 × the wet concrete volume you want to produce.