Cement Slab Calculator — Bags of Cement Needed

🏠 Cement Slab Calculator

Slab Length (m)

Slab Width (m)

Slab Thickness (cm)

Concrete Mix Ratio

Cement Bags per m³ by Mix Ratio

1:1.5:3 (M20)	~29 bags / m³
1:2:4 (M15)	~23 bags / m³
1:3:6 (M10)	~16 bags / m³
1:4:8 (M7.5)	~12 bags / m³

How to Calculate Cement for a Concrete Slab

The amount of cement needed depends on the slab volume and the concrete mix ratio. The most common mix for residential slabs is M20 (1:1.5:3) — 1 part cement, 1.5 parts sand, 3 parts aggregate.

Step-by-Step Calculation

Calculate slab volume: L × W × T (in meters)
Apply dry volume factor: × 1.54 (accounts for voids)
Find cement fraction: Divide by sum of mix ratio parts
Convert to bags: 1 bag (50 kg) = 0.035 m³ of cement

Example: 5×4×0.15 m slab with 1:1.5:3 mix
Volume = 3 m³ → Dry = 3 × 1.54 = 4.62 m³
Cement = 4.62 × (1/5.5) = 0.84 m³ → 24 bags

Need full material quantities (sand + aggregate too)?

Open Mix Ratio Calculator →

Frequently Asked Questions

What mix ratio should I use for a house slab?+

For a standard residential slab, use M20 (1:1.5:3). For driveways or light-duty floors, M15 (1:2:4) is acceptable. For structural elements, use M25 or higher and consult an engineer.

Why multiply by 1.54 for dry volume?+

When dry materials (cement, sand, aggregate) are mixed with water, they compact and reduce in volume by about 35%. To get 1 m³ of wet concrete, you need 1.54 m³ of dry materials.

How many kg in a bag of cement?+

Standard bags are 50 kg in most countries. In the USA, bags are typically 94 lbs (42.6 kg) or 60 lbs (27.2 kg). Our calculator uses 50 kg bags.