Ordering the right amount of soil
Topsoil is the base of every new bed, raised bed and lawn, and it is heavy and awkward to move twice. Ordering the right amount the first time saves a second delivery or a pile left over on the drive.
This topsoil calculator turns the size of the area and the depth of soil into cubic yards, cubic feet and cubic metres, adds an allowance for the soil settling once it is watered, and counts the bags you would need instead of a bulk load.
How to use it
- Measure the area. Split L shapes into rectangles, and use the circle mode for round beds.
- Choose the depth of new soil. Lawns often need a few inches; raised beds and new vegetable beds need more.
- Keep the 10% settling allowance, or change it. Firm, damp soil settles less than loose, dry soil.
- Read the cubic yards for a bulk order, or the number of bags for your bag size.
The topsoil formula
cubic feet = length (ft) × width (ft) × depth (in) ÷ 12
with settling: cubic feet × (1 + allowance)
cubic yards = cubic feet ÷ 27Depth goes in inches and the area in feet, so dividing by 12 puts everything in feet. Bulk soil is usually sold by the cubic yard in the US and by the cubic metre or bulk bag elsewhere.
Worked example: a 20 by 10 foot bed, 4 inches deep
- Area: 20 × 10 = 200 ft²
- Volume: 200 × 4 ÷ 12 = 66.67 cubic feet
- With 10% for settling: 73.33 cubic feet
- In cubic yards: 73.33 ÷ 27 = 2.72 cubic yards
- In 1 cubic foot bags: 74 bags
Order about 2.72 cubic yards, or 74 bags of 1 cubic foot. At this size a bulk delivery is usually cheaper and much less work than carrying dozens of bags.
Area covered by one cubic yard
| Depth | Covers |
|---|---|
| 2 inches | 162 ft² |
| 4 inches | 81 ft² |
| 6 inches | 54 ft² |
For a raised bed, measure the inside of the frame and fill to just below the top, since watering will lower the level.
Bulk or bagged?
Bagged soil is easy to carry and store, and suits small beds and containers. Bulk soil comes loose by the cubic yard or in large bulk bags, costs less per yard, and suits new lawns and big beds. Compare prices using the cubic yards above, and add any delivery charge to the bulk price.
Before the soil arrives
- Clear weeds and loosen the ground underneath, so roots can reach down.
- Ask the supplier whether the soil is screened and what it contains.
- For mulch on top of new beds, see the mulch calculator; for stone, the gravel calculator.
Frequently asked questions
How much topsoil do I need?
Multiply the length by the width in feet, then by the depth in inches, and divide by 12 for cubic feet. Divide by 27 for cubic yards, then add an allowance for settling. A 20 by 10 foot bed at 4 inches deep needs about 2.72 cubic yards with a 10% allowance.
How many bags of topsoil are in a cubic yard?
A cubic yard is 27 cubic feet, so it equals 27 bags of 1 cubic foot, 36 bags of 0.75 cubic feet, or 13.5 bags of 2 cubic feet. Always round up to whole bags. Choose your bag size above and the calculator counts them for you.
Why add extra topsoil for settling?
Loose soil has air in it. Once it is watered, rained on and walked over, it packs down and the level drops. Adding a margin, often around 10%, means the finished bed ends up at the height you planned rather than a little low. Set it to 0 if your soil is already firm.
How deep should topsoil be?
It depends on the job. Topping up a lawn needs only a thin layer, new lawns from seed or turf need a few inches, and vegetable beds and raised beds need more for roots to grow. Your supplier or a local garden centre can advise for your soil and plants.
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