Garden SurveyorRetaining Wall Calculator
Sleepers, blocks or gabions with drainage gravel and membrane.
3 advanced inputs hidden. Switch to Advanced to fine-tune.
Order what you need for this job
Dense concrete blocks (7N)
Building Materials Nationwide
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Heavy-duty weed-control membrane
Amazon
£15–£40 / roll
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- Wall length
- 5m
- Wall height
- 600mm
- Sleepers
- 7
- Posts
- 6
- Drainage gravel
- 2.25t
- Geotextile membrane
- 4m²
Heads-up: Drainage behind the wall is not optional: a perforated land drain wrapped in geotextile and backfilled with 20 mm clean stone, exiting to daylight or a soakaway. Why it matters: Without drainage, hydrostatic pressure builds behind the wall and pushes it over within a few winters.
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Essentials for this job
Quantities include a ~10% waste allowance. Guide prices are indicative UK ranges (materials only, inc. VAT) — always confirm with the supplier before ordering.
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Ad · Some links are sponsored. We may earn a small commission at no extra cost to you. Suppliers are chosen for fit, not commission.
This app provides general UK guidance and material estimates only. It is not legal, planning, engineering or building-control advice. Always confirm requirements with your local planning authority, building control, utility providers, manufacturers or qualified professionals.
Worked example
A 6.0 m sleeper retaining wall, 600 mm high, holding back clay.
Inputs
- Wall type
- Timber sleeper
- Length
- 6.0 m
- Height
- 600 mm
- Soil
- Clay
| Step | Working | Result |
|---|---|---|
| Courses | 600 mm height ÷ 200 mm sleeper depth = 3 courses | 600 mm |
| Sleepers | 3 courses × 6.0 m ÷ 2.4 m sleeper length | 8 |
| Posts | one post roughly every 1.2 m of wall | 6 |
| Drainage gravel | 300 mm wide free-draining backfill behind the wall | 2.7 t |
| What to order | Quantity |
|---|---|
| Sleepers | 8 |
| Posts | 6 |
| Drainage gravel | 2.7 t |
| Geotextile membrane | 5 m² |
In short: Order 8 sleepers, 6 posts, 2.7 t of clean drainage stone and 5 m² of geotextile behind the wall.