Solve backwards
How long a French drain will my gravel fill?
- 3 yd³The example worked below
- French Drain Gravel CalculatorEvery figure is its own
You have
How much drainage gravel?
That is 3 yd³(2.3 m³). Worked by the French Drain Gravel Calculator at the settings below.
The settings it uses
- Trench Width
- 11.8 in
- Trench Depth
- 18 in
- Drain Pipe Diameter
- 4 in
What it will do
Enough for 53.3 ft of French drain.
One French drain. Enough for 53.3 ft of French drain.
Or several. About 1 French drain of the size the French Drain Gravel Calculator opens on: 49 ft of French drain.
Check it forwards
- Trench Length
- 53.3 ft
- It asks for
- 3 yd³
- You have
- 3 yd³
The French Drain Gravel Calculator asks for 3 yd³ at that size.
If you had more, or less
Around your amount
Each worked by the French Drain Gravel Calculator at the same settings.
Half
1.5 yd³
26.7 ft of French drain
Yours
3 yd³
53.3 ft of French drain
Half as much again
4.5 yd³
80 ft of French drain
Double
6 yd³
107 ft of French drain
Common amounts
What each amount of drainage gravel covers
The sizes it is usually sold in, each worked by the French Drain Gravel Calculator at the settings above.
| You have | It covers | As one French drain | Average French drains |
|---|---|---|---|
| 1 yd³(0.8 m³) | — | 17.8 ft of French drain | under 1 |
| 2 yd³(1.5 m³) | — | 35.5 ft of French drain | under 1 |
| 3 yd³(2.3 m³) | — | 53.3 ft of French drain | 1 |
| 5 yd³(3.8 m³) | — | 88.8 ft of French drain | 1 |
A trench a spade wide and knee deep
The calculator opens at a trench 12 inches wide and 18 inches deep, about 30 by 46 cm — a common minimum for hand-digging and a typical residential yard drain — around 4 inch (100 mm) perforated pipe. Stone does not fill the space the pipe takes, so the pipe's volume comes off the trench before the gravel is counted.
Dig to the average depth
The trench is modelled at one depth, so a run laid to fall is only right if you enter its average depth. A 15 m (49 ft) run at the usual 1 per cent fall finishes 150 mm (6 in) deeper than it starts, and a trench read at its shallow upstream end holds about 16 per cent more gravel than the figure — so fewer feet of drain than shown.
A soil cap takes some of the depth
Gravel is taken to the full depth, trench floor to ground level. A topsoil or turf cap over the stone comes off that depth — a 4 inch (100 mm) cap on an 18 inch (460 mm) trench is over a fifth of the volume — so the same gravel fills a longer run. Filter fabric round the stone is a separate order.
How the answer is worked
Nothing here is a second formula. The French Drain Gravel Calculator runs forwards — a size in, a quantity out — and this page grows its own starting French drain 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.
French Drain Gravel Calculator
runs it forwardsEstimate the gravel backfill a French drain trench needs, in cubic yards or cubic metres, net of the drain pipe's own volume.
Work out what to buy insteadSolve backwards
Other things you might already have
How big a bed will my bags of mulch cover?
Bagged mulch, worked by the Mulch Calculator.
How much bed will a yard of mulch cover?
Bulk mulch, worked by the Mulch & Gravel Calculator.
How much ground will my gravel cover?
Gravel, worked by the Mulch & Gravel Calculator.
How big a bed will my topsoil fill?
Topsoil, worked by the Topsoil Calculator.
How big a raised bed will my soil fill?
Raised bed soil, worked by the Garden Soil Calculator.
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 French drain does 3 yd³ of drainage gravel cover?
- At the French Drain Gravel Calculator's own settings: Enough for 53.3 ft of French drain. That is about 1 French drain of the size the calculator opens on: 49 ft of French drain. Every figure follows the settings, which you can change in the calculator.
- How much French drain does 2 m³ of drainage gravel cover?
- At the French Drain Gravel Calculator's own settings: Enough for 14 m of French drain. Every figure follows the settings, which you can change in the calculator.
- How much gravel does a French drain need per foot?
- For a 12 by 18 inch trench around a 4 inch pipe, about 1.4 cubic feet per foot of run — roughly a cubic yard for every 19 to 20 feet, or a cubic metre for every 7 metres or so, before a ten per cent allowance for ragged walls and settling.
- How much does a yard of drainage gravel weigh?
- Clean drainage gravel is commonly quoted near 1.5 tonnes per cubic metre, about 1.3 short tons per cubic yard. Quarries weigh stone rather than measuring it, so ask for the volume or the density of the stone you are buying before converting a ticket.
- Does a bigger pipe need less gravel?
- Slightly — the pipe displaces stone. Going from a 4 inch to a 6 inch pipe over 49 feet (15 m) saves only about a fifth of a cubic yard, and it settles none of the drainage questions: capacity depends on the catchment, rainfall, gradient and soil, not on the stone.