How many cement bags are needed per m³ of concrete?

For standard concrete (250 kg/m³ mix), you need 5 bags of 50 kg per m³. For structural concrete (300 kg/m³), use 6 bags. This calculator uses the typical dosage for each element type.

Why should I add a wastage percentage?

On-site losses from spillage, unusable mixes and level corrections always occur. Adding 5–10 % to your final order ensures you don't run short of material.

What is the difference between mass concrete and reinforced concrete?

Mass concrete has no steel reinforcement and is used for low-load foundations. Reinforced concrete includes steel bars that provide tensile strength, making it suitable for slabs, columns and beams.

Retaining Wall Calculator

Last updated: 2026-05-09

Use the Retaining Wall Calculator to get instant, accurate results. Enter your values below.

Inputs

Dimensions

Wall length (m) (m)

Wall height (m) (m)

Base thickness (m) (m)

Crown thickness (m) (m)

Wastage Allowance (%)

Result

Enter values and press Calculate

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Common Sizes — Click to Fill

area	coats
20	1
30	2
40	2
60	2
80	3

Popular combinations

Retaining Wall 3m Long 1.0m High – Concrete Retaining Wall 3m Long 2.5m High – Concrete Retaining Wall 5m Long 2.0m High – Concrete Retaining Wall 10m Long 1.0m High – Concrete Retaining Wall 10m Long 2.5m High – Concrete Retaining Wall 15m Long 2.0m High – Concrete Retaining Wall 20m Long 1.5m High – Concrete Retaining Wall 20m Long 3.0m High – Concrete

What is a Retaining Wall?

A retaining wall holds back soil at a change in ground level. Common types include gravity walls, cantilever walls, and counterfort walls. This calculator estimates concrete, steel and formwork for cantilever retaining walls — the most common type in residential and commercial construction.

Volume Calculation

Volume = Length × Height × Base thickness (simplified)

The wall has two main components: the stem (vertical part) and the base slab. Total concrete includes both plus a key at the base for sliding resistance. Typical stem thickness: 250-400mm. Base width: 40-60% of wall height.

Worked Example

Retaining wall 10m long, 3m high, 0.30m stem thickness:

Stem volume = 10 × 3 × 0.30 = 9 m³
Base volume = 10 × 1.80 × 0.30 = 5.4 m³
Total concrete = 14.4 m³
Cement = 14.4 × 7 = 101 bags
Steel = 100-150 kg/m³ depending on height
Formwork = stem area both sides + base edges

Common Mistakes

Insufficient drainage behind the wall (no gravel backfill or weep holes)
Base too narrow causing overturning
No structural key at base for sliding resistance on clay soils
Not accounting for surcharge loads from vehicles or adjacent structures

Standards

Calculated per EN 1992-1-1 / EN 1997-1.

Written and reviewed by the CalcToWork editorial team. Last updated: 2026-05-09.