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Septic & DrainageCalculators

Drainage

Drainage Stone Calculator

For any rectangular bed of stone — a dry well surround, a splash strip, a gravel drainage layer — enter the footprint and depth to get volume in cubic feet and cubic yards plus an estimated tonnage at the density you choose.

Your measurements

Results update as you type. Every unit dropdown converts for you.

Presets fill the density field with a common supplier figure. You can overwrite it.

%

Stone to order

1.09cubic yards

Volume in cubic feet
29.33 cu ft
Estimated weight
1.52 tons
Bed volume before waste
26.67 cu ft
Density used
2,800 lb per cubic yard
Waste allowance used
10%
Show the calculationOpen
  1. Bed volume20.00 ft × 4.00 ft × 0.333 ft=26.67 cu ft
  2. With waste allowance26.67 × (1 + 10 ÷ 100)=29.33 cu ft
  3. Convert to cubic yards29.33 ÷ 27=1.09 cu yd
  4. Estimated tons1.09 cu yd × 1.40 tons/yd³=1.52 tons

Reading your result

Cubic yards is the ordering figure; tons is the same volume weighed at the density you chose. Which one you use depends on how your supplier bills.

The volume shown includes your waste allowance. The bed volume before waste is listed separately so you can see how much of the order is contingency.

On small beds, delivery minimums often decide the quantity anyway. If the result is well under a yard, ask what the minimum load is before optimising the number.

How this calculator works

The volume is length times width times depth, with depth usually entered in inches since stone layers are shallow relative to their footprint.

The material preset fills the density field with a typical supplier figure. It stays editable, because the real weight depends on stone size, fines content and how wet the pile is when it is loaded.

Waste allowance is added after the volume is calculated. Stone spread over soft ground works down into it, and depth on a spread bed is never as even as it is on paper.

Tonnage is derived from cubic yards times density. If your supplier sells by the ton, that is the number to order against; if they sell by the yard, use the cubic yard figure and treat tonnage as a check on delivery weight.

The formula

Bed volume
length × width × depth
Order volume
bed volume × (1 + waste ÷ 100)
Cubic yards
cubic feet ÷ 27
Estimated tons
cubic yards × density in tons per cubic yard

Worked example

A 20 ft by 4 ft stone bed, 4 inches deep, with a 10% waste allowance and stone at 1.4 tons per cubic yard.

  1. 01Convert depth4 in ÷ 12=0.333 ft
  2. 02Bed volume20 × 4 × 0.333=26.67 cu ft
  3. 03Add 10% waste26.67 × 1.10=29.33 cu ft
  4. 04Cubic yards29.33 ÷ 27=1.09 cu yd
  5. 05Estimated tons1.09 × 1.4=1.52 tons

Order about 1.1 cubic yards, roughly 1.5 tons. On small orders like this, delivery minimums often decide the quantity anyway.

How to take the measurements

  • Measure the footprint the stone will actually cover, not the whole work area.
  • Decide the finished depth first. A shallow decorative layer and a functional drainage layer are very different quantities over the same footprint.
  • For irregular shapes, break the area into rectangles, calculate each one, and add the results.
  • Ask your supplier what the material weighs per cubic yard and enter that figure rather than relying on a preset.
  • Check whether the price is per ton or per yard before you order — mixing the two is the most common way to end up with the wrong quantity.

Practical considerations

  • Price per yard and price per ton can look very different for the same material. Convert both to one unit before comparing suppliers.
  • Delivery access decides more than people expect. A truck that cannot reach the work area means the whole load gets handled twice.
  • Stone placed directly on bare soil migrates into it over time and the layer thins. That is a maintenance cost, not just an installation detail.
  • Take it in one delivery where you can. Split loads from different batches can differ visibly in colour and gradation.

Assumptions and limitations

  • The calculation assumes a uniform depth over a rectangular footprint. Real spread depth varies, which is what the waste allowance is for.
  • Density presets are typical figures, not measurements of your material. They are editable for that reason.
  • Nothing here addresses whether stone is the right material, what gradation suits the application, or whether fabric is needed.

Frequently asked questions

How deep should a drainage stone layer be?

It depends entirely on what the layer is doing. A decorative surface layer is shallow; a stone envelope around drainage pipe is much deeper. Set the depth from your design and let the calculator handle the arithmetic.

What does drainage stone weigh per yard?

Commonly quoted figures for clean washed stone sit near 1.4 tons per cubic yard, with material containing fines running heavier and wet material heavier still. Your supplier's own figure is the one to use.

Should I order by the yard or by the ton?

Order in whichever unit your supplier bills in. The calculator gives both so you can compare quotes on the same basis.

Do I need fabric under the stone?

That is a design decision this calculator does not weigh in on. Fabric is a common way to keep stone and soil from mixing, but whether to use it depends on your soil and application.

How deep should a drainage stone layer be?

It depends entirely on what the layer does. A decorative surface course is shallow; a stone envelope around drainage pipe is much deeper. Take the depth from your design and let the calculator handle the arithmetic.

Should I order by the yard or by the ton?

Whichever your supplier bills in. The calculator gives both so you can compare quotes on the same basis.

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