Soil Calculator
Find how much soil you need for a raised bed, a garden bed, or a pot, and how many bags to buy. It works for topsoil, garden soil, potting mix, and fill dirt. Enter each area's shape, size, and depth. For bark or wood chips to spread on top, use the Mulch Calculator.
Add more beds or pots, or subtract areas that need no soil, such as a path.
- Choose US or Metric. This also sets the bag sizes in the results: 2, 1.5, and 0.75 cu ft bags for US, and 750 to 25 L bags for Metric.
- Pick the shape of the area and enter its dimensions and Depth. For a raised bed, measure the inside of the frame, and enter how deep you want to fill it with soil. For a round pot, choose Circle and enter the inside diameter.
- Use Add section for each extra bed or pot. Set a section to Subtract for parts that need no soil, such as a path.
- Keep the 10% waste allowance or change it. If you change it, Reset to 10% brings it back.
- If your bag size is not listed, enter the volume printed on the bag in Custom bag size. Some bags of topsoil show the weight, such as 40 lb, in large print. Look for the volume in cu ft or liters on the bag.
- Optionally, enter a price per bag, per cubic yard, cubic foot, or cubic meter, or per US ton or tonne to estimate the cost. A price per US ton or tonne needs a Density.
The dimension and depth fields accept whole numbers, decimals, fractions,
and mixed numbers, such as 12, 10.5,
3/4, or 2 1/2. Choose ft + in
as the unit to enter a length such as 12 ft 6 in in two fields.
How much soil you need
The volume of soil for an even depth is:
Volume = area × depth
Convert every dimension to the same unit before you multiply. With dimensions in feet, divide cubic feet by 27 to get cubic yards. The waste allowance is added after subtracting any sections: total = net volume × (1 + waste % ÷ 100).
The number of bags is:
Bags = total volume ÷ volume per bag, rounded up
Bagged soil is sold by volume, and the volume on the bag is the loose volume you fill with. The calculator shows these common bag sizes:
| Bag | Examples |
|---|---|
| 2 ft³ | Kellogg Garden Organics Raised Bed & Potting Mix |
| 1.5 ft³ | Miracle-Gro All Purpose Garden Soil, Raised Bed and Garden Soil |
| 0.75 ft³ | Scotts Premium Topsoil |
| 750 L | Rolawn Blended Loam Topsoil bulk bag (UK) |
| 100 L | Verve Peat Free Multi Purpose Compost (UK) |
| 50 L | Westland Peat Free Multi-Purpose Compost with John Innes (UK) |
| 35 L | Rolawn Blended Loam Topsoil Handy Bags (UK) |
| 25 L | Westland Multi-Purpose Compost with John Innes (UK) |
The results also show the volume in liters, which helps for pots and planters, where potting mix is often sold by the liter.
Extra soil for settling
Soil settles after you fill a bed and water it. The soil maker Kellogg Garden Products notes that soil settles over time and after watering, and suggests ordering 10 to 15% extra. The calculator starts at 10%.
Settling goes on after the first season. University of Illinois Extension calls it a fact of raised bed gardening and suggests topping up raised beds each year, so plan for more soil later.
How much soil weighs
The weight of soil depends on the type of soil and how wet it is. The UK topsoil supplier Rolawn says one tonne of standard topsoil is about 0.67 m³, which works out to about 1.49 t/m³. A 500 L bulk bag of topsoil made by Rolawn is listed at 470 kg, which works out to about 0.94 t/m³. Rolawn also notes that density varies with the type of topsoil and its make-up, and recommends working out topsoil by volume.
These two figures give a range of about 0.9 to 1.5 t/m³ (about 56 to 94 lb/ft³), and your soil may fall outside it. The calculator has no default density. If your supplier sells by the ton or tonne, ask for the density of its soil and enter it under Weight to see the weight and the cost.
With a density entered, the calculator works out the weight as:
Weight = total volume × density
Examples
A 4 × 8 raised bed
A raised bed 8 ft × 4 ft inside, filled 12 in deep, is 32 ft³. With a 10% waste allowance, the total is 35.2 ft³, or 1.30 yd³. That is 18 bags of 2 cu ft (35.2 ÷ 2 = 17.6, rounded up), 24 bags of 1.5 cu ft, or 47 bags of 0.75 cu ft. At $5.00 per 1.5 cu ft bag, the cost is $120.00.
A pot
A round pot 16 in across inside, filled 14 in deep, holds 1.63 ft³. With 10% added, that is 1.79 ft³, or 50.74 L: one 2 cu ft bag.
Metric dimensions
A bed 2.4 m × 1.2 m, filled 30 cm deep, is 0.864 m³. With 10% added, the total is 950.4 L, shown as 0.95 m³. That is 2 bulk bags of 750 L, or 20 bags of 50 L. At a density of 1.5 t/m³, it weighs 1.43 tonnes.
FAQ
18 bags of 2 cu ft or 24 bags of 1.5 cu ft, for a bed filled 12 in deep. The bed needs 32 ft³, or 35.2 ft³ with 10% extra. For a 6 in deep bed, halve it.
A cubic yard is 27 ft³, so it takes 13.5 bags of 2 cu ft (buy 14), 18 bags of 1.5 cu ft, or 36 bags of 0.75 cu ft.
About 0.8 to 1.3 US tons, depending on the soil and how wet it is. At Rolawn's figure of one tonne per 0.67 m³, a cubic yard weighs about 1.26 US tons (2,516 lb). At 0.94 t/m³, it weighs about 0.79 US tons (1,584 lb). Ask your supplier for the density of its soil.
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