How many bricks per m²?

With a standard brick (24 × 11.5 cm) and a 1 cm joint, you get approx. 38–40 bricks per m² for a half-brick wall. For a full-brick wall, multiply by 2.

How do I deduct windows and doors?

Subtract the area of each opening (width × height) from the total before entering it in the calculator. Standard door: 0.9 × 2.1 m = 1.89 m². Windows: as measured.

What mortar mix is used in brickwork?

The most common ratio is 1:4 (cement:sand) for external walls and 1:5 for internal walls. This calculator gives you the cement and sand quantities directly.

Retaining Wall Calculator

Last updated: 2026-05-07

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

Inputs

Result

Enter values and press Calculate

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Common Sizes — Click to Fill

	Wall length (m)	Block length (cm)	Block height (cm)	Wall height (m)
Small wall	3 m	20 cm	0.2 cm	0.9 m
Medium wall	4.5 m	20 cm	0.2 cm	0.9 m
Large wall	6 m	20 cm	0.2 cm	0.9 m
Room	9 m	20 cm	0.2 cm	0.9 m
House perimeter	12 m	20 cm	0.2 cm	0.9 m

What is the Retaining Wall Calculator?

Retaining walls hold back soil on sloped sites — and building one without enough drainage or structural blocks leads to wall failure and costly repair. This calculator computes the total number of concrete blocks needed for your wall dimensions, plus the volume of drainage gravel to place behind the wall for water management.

You may also find the Concrete Steps Calculator, Drywall Calculator, and Paver Calculator useful.

Who Uses This Calculator?

This tool is used by homeowners landscaping a sloped yard, landscapers building garden retaining walls, and civil engineers specifying low-height retaining structures.

How to Use the Retaining Wall Calculator

Enter your Wall length.
Enter your Wall height.
Enter your Block length.
Enter your Block height.
Click Calculate to see your results instantly.

Formula

The calculator uses the following formula:

Blocks = ceil(length ÷ block_L) × ceil(height ÷ block_H); Gravel = length × base_depth × 0.6

Worked Example

A 6 m long × 0.9 m high retaining wall using 400 mm × 200 mm blocks needs approximately 68 blocks plus 1.08 m³ of drainage gravel behind it.

Step-by-Step Calculation

Courses high: ceil(0.9 m ÷ 0.2 m) = 5 courses
Blocks per course: ceil(6 m ÷ 0.4 m) = 15 blocks
Total blocks: 15 × 5 = 75 blocks
Base gravel depth: 20 cm; Volume: 6 × 0.6 × 0.2 = 0.72 m³ ≈ 1.1 tonnes

Common Mistakes to Avoid

Not burying the first course below grade — minimum 10% of wall height
Forgetting drainage pipe and gravel backfill behind the wall
Using standard blocks instead of approved retaining wall blocks for walls > 90 cm

Pro Tip: Every retaining wall needs drainage — a perforated pipe at the base wrapped in geofabric, backfilled with 200–300 mm of 20 mm aggregate. Without it, water pressure will push the wall over within a few years.

Frequently Asked Questions

How high can a retaining wall be without engineering?

Most councils allow retaining walls up to 600–900 mm high without engineering certification. Walls above 1 m typically require a structural engineer's design and council approval. Always check local regulations.

What is the best block type for a retaining wall?

Concrete segmental retaining wall blocks (SRW blocks) are the most common for DIY. They interlock without mortar and are designed for retaining walls. Sizes typically range from 200 × 100 × 200 mm to 450 × 200 × 250 mm.

How much batter (lean) should a retaining wall have?

A batter of 1:10 (10 mm per 100 mm of height) is standard for segmental block walls. This lean-back improves stability by shifting the wall's centre of gravity toward the retained soil.

What type of gravel do I use behind a retaining wall?

Use clean 20 mm crushed rock or gravel (no fines). Fines compact and retain water, defeating the purpose. The drainage layer should be at least 300 mm wide, wrapped in geofabric to prevent soil ingress.

How many courses of blocks per metre of wall height?

This depends on block height. 200 mm blocks give 5 courses per metre, 100 mm blocks give 10 courses per metre. Calculate: height (mm) ÷ block height (mm) = number of courses.

Written and reviewed by the CalcToWork editorial team. Last updated: 2026-05-07.