Solve backwards
How long a retaining wall will my drainage gravel back?
- 5 yd³The example worked below
- Retaining Wall Drainage Gravel CalculatorEvery figure is its own
You have
How much retaining wall drainage stone?
That is 5 yd³(3.8 m³). Worked by the Retaining Wall Drainage Gravel Calculator at the settings below.
The settings it uses
- Wall Height
- 4 ft
- Drainage Zone Width
- 11.8 in
- Spillage and Settlement Allowance (%)
- 10
What it will do
Enough for 31.3 ft of retaining wall 4 ft high.
One retaining wall. Enough for 31.3 ft of retaining wall 4 ft high.
Or several. Less than one retaining wall of the size the Retaining Wall Drainage Gravel Calculator opens on (49 ft of retaining wall 4 ft high).
Check it forwards
- Wall Length
- 31.3 ft
- It asks for
- 5 yd³
- You have
- 5 yd³
The Retaining Wall Drainage Gravel Calculator asks for 5 yd³ at that size.
If you had more, or less
Around your amount
Each worked by the Retaining Wall Drainage Gravel Calculator at the same settings.
Half
2.5 yd³
15.7 ft of retaining wall 4 ft high
Yours
5 yd³
31.3 ft of retaining wall 4 ft high
Half as much again
7.5 yd³
47 ft of retaining wall 4 ft high
Double
10 yd³
62.7 ft of retaining wall 4 ft high
Common amounts
What each amount of retaining wall drainage stone covers
The sizes it is usually sold in, each worked by the Retaining Wall Drainage Gravel Calculator at the settings above.
| You have | It covers | As one retaining wall | Average retaining walls |
|---|---|---|---|
| 2 yd³(1.5 m³) | — | 12.5 ft of retaining wall 4 ft high | under 1 |
| 5 yd³(3.8 m³) | — | 31.3 ft of retaining wall 4 ft high | under 1 |
| 10 yd³(7.6 m³) | — | 62.7 ft of retaining wall 4 ft high | 1 |
| 15 yd³(11.5 m³) | — | 94 ft of retaining wall 4 ft high | 1 |
The full height, buried courses included
The drainage zone runs from the top of the wall down to the base course, not just the exposed face. A wall with buried courses — commonly a tenth of the wall on a segmental block job — needs those counted in the height, or the stone comes up short by exactly the embedment, and it is the bottom of the zone that has to drain.
Twelve inches behind the block
Twelve inches, 30 cm, is a commonly recommended minimum drainage zone width for segmental retaining walls, and the calculator opens there. An excavation cut wider than that takes the difference on top, so measure the cut rather than trusting the zone width; ten per cent more covers what spills from the barrow and settles as it is tamped.
Fabric keeps it draining
The zone only works while silt is kept out of it. With no filter fabric between the stone and the retained soil, fines wash into the voids over a few seasons and the stone locks up — a clogged zone holds water exactly as if there were none. Above about 4 feet (1.2 m) of exposed wall, or with a load behind it, the wall needs an engineered design.
How the answer is worked
Nothing here is a second formula. The Retaining Wall Drainage Gravel Calculator runs forwards — a size in, a quantity out — and this page grows its own starting retaining wall in proportion until the quantity it asks for is what you have. Where it rounds up to whole containers, the answer is the largest size before the next one would be needed.
Where the calculator adds an allowance for cuts or breakage when you order, the same allowance comes off here, because it is the same calculator: a stack you already own finishes less than its face value. Where it adds none, neither does this page — the settings beside the answer say which.
Retaining Wall Drainage Gravel Calculator
runs it forwardsEstimate the drainage gravel needed behind a retaining wall, in cubic yards or cubic metres.
Work out what to buy insteadSolve backwards
Other things you might already have
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How much ground will my gravel cover?
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How big a bed will my topsoil fill?
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How big a raised bed will my soil fill?
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How much ground will my compost dress?
Compost, worked by the Compost Blend Calculator.
Solve backwards
Start from what is already in the yard
Paint, sheets, rolls, bags and pieces, each read the other way by the calculator that orders it.
The calculator's own figures
Nothing is estimated twice: the page runs the same calculator you would order with.
The largest size that fits
Where a calculator rounds up to whole containers, the answer stops before the next one.
Both unit systems
Gallons and litres, square feet and square metres, side by side.
Frequently asked questions
- How much retaining wall does 5 yd³ of retaining wall drainage stone cover?
- At the Retaining Wall Drainage Gravel Calculator's own settings: Enough for 31.3 ft of retaining wall 4 ft high. Every figure follows the settings, which you can change in the calculator.
- How much retaining wall does 4 m³ of retaining wall drainage stone cover?
- At the Retaining Wall Drainage Gravel Calculator's own settings: Enough for 10.1 m of retaining wall 1.2 m high. Every figure follows the settings, which you can change in the calculator.
- How much gravel goes behind a retaining wall?
- A zone about 12 inches (30 cm) wide, the full height of the wall including buried courses. For a 4 foot (1.2 m) high wall that is 4 cubic feet per foot of wall — a cubic yard for about every 6 to 7 feet, or a cubic metre for every 2.8 metres or so, before a ten per cent allowance.
- What kind of gravel goes behind a retaining wall?
- Clean, angular crushed stone with no fines, so water can drain through it freely and it locks together as it is tamped in lifts. It is wrapped from the retained soil with filter fabric so silt cannot wash into it and clog the voids.
- When does a retaining wall need an engineer?
- Above roughly 4 feet (1.2 m) of exposed height for an unreinforced segmental wall, or at any height with a slope, a driveway or a structure loading the ground behind it. Those walls usually need geogrid reaching well back into compacted structural fill — a different material and a far larger volume than drainage stone.