Retaining Wall Calculator — Estimate Your Materials
Use this guide to estimate the number of concrete sleepers and steel posts required for your retaining wall. These figures are indicative — always confirm quantities with your builder or engineer before ordering, particularly for walls over 1.0m or on reactive clay soils.
How to Calculate Concrete Sleepers
Concrete sleepers are typically 2000mm (2.0m) long. To calculate the number of sleepers per course:
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Wall length ÷ 2.0m = sleepers per course (round up to the nearest whole number)
- Multiply by the number of courses (wall height ÷ sleeper thickness)
Sleeper Thickness Reference
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75mm sleepers — standard residential; 1000mm wall height = 13–14 courses
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100mm sleepers — heavy duty; 1000mm wall height = 10 courses
Example Calculation
Wall: 10m long × 1.0m high using 75mm sleepers
- Sleepers per course: 10m ÷ 2.0m = 5 sleepers
- Number of courses: 1000mm ÷ 75mm = 13.3 → 14 courses
- Total sleepers: 5 × 14 = 70 sleepers
How to Calculate Steel Posts
Steel posts are typically spaced at 2.0m centres (one post per sleeper joint). For a 10m wall:
- 10m ÷ 2.0m = 5 spans = 6 posts (always add 1 for the end post)
Post Length Reference
Post length = wall height above ground + embedment depth. Embedment depth is typically 1.5× the exposed wall height for standard soils, and up to 2.0× for reactive clay. For a 1.0m wall in standard soil: 1.0m + 1.5m = 2.5m post minimum. Read our Post Embedment Depth Guide for full detail.
Post Series Selection Guide
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100 Series posts — walls up to ~1.0m in stable, well-drained soils → Shop 100 Series
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150 Series posts — walls 1.0m–1.8m or reactive clay sites → Shop 150 Series
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200 Series posts — walls over 1.8m or engineered applications → Shop 200 Series
Important Notes
- These calculations are a guide only. Retaining walls over 1.0m in height require a structural engineer's assessment in most Australian states and territories.
- Reactive clay soils, sloping sites, and surcharge loads (driveways, structures) all affect post sizing and spacing requirements.
- Always check your local council requirements before commencing construction. See our Retaining Wall Regulations — State-by-State Guide.
Get an Accurate Quote
For a precise material estimate with delivery cost to your site, → Book a Free Quote. Our team will confirm quantities, post sizing, and delivery timeframe within 24 hours.
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