Topsoil calculator: cubic yards, bags and raised beds

Quick answer

A raised bed of 8 × 4 ft filled 12 in deep holds 32 cu ft, which is 1.19 cubic yards or 22 bags of 1.5 cu ft before any allowance. One cubic yard of topsoil covers 81 sq ft 4 in deep, or 324 sq ft 1 in deep.

What this calculator does

It calculates the soil for a layer over an area, such as a new lawn or a garden bed, or to fill one or more identical raised beds. It gives the volume to order in cubic yards or cubic metres, the number of bags or bulk bags, and an approximate weight for transport.

The volume is exact geometry. The weight depends on the soil and how wet it is, so it is an estimate. Bagged raised bed mixes are sold by volume, so for those only the volume and the bags matter.

How to use it

1. Choose metric or US units. In US units you can type feet and inches, such as 7' 10", and fractions.
2. Choose Area or Raised beds.
3. Area: enter the length, the width and the depth of soil. Raised beds: enter the inside length and width of one bed, the depth of soil and the number of beds.
4. Check the bulk density and the bag size against your product or supplier.
5. Set the allowance for settling and select Calculate.

How the result is calculated

1. Volume = length × width × depth, times the number of beds.
2. Volume to order = volume × (1 + allowance ÷ 100), rounded up to 0.01 m³ or 0.01 cubic yard.
3. Bags = volume to order ÷ volume of one bag, rounded up to a whole bag.
4. Weight = volume to order × bulk density, rounded up to 0.01 tonne or short ton.

The depth is entered in millimetres or inches and converted. One cubic yard is 27 cu ft; one cubic metre is 1000 L.

Worked example

An area of 5 m by 3 m gets 100 mm of topsoil: 5 × 3 × 0.1 = 1.5 m³. With 10 percent allowance: 1.65 m³. In bulk bags of 750 L: 1650 ÷ 750 = 2.2, so 3 bulk bags. At 1400 kg per m³ the soil weighs 2310 kg, or 2.31 t.

In US units: 15 ft by 10 ft at 4 in deep is 15 × 10 × (4 ÷ 12) = 50 cu ft. With 10 percent allowance: 55 cu ft, which is 2.04 cubic yards. In bags of 0.75 cu ft: 55 ÷ 0.75 = 73.3, so 74 bags. At 87 lb per cu ft the weight is 4785 lb, or 2.4 short tons.

Two raised beds of 8 ft by 4 ft filled 12 in deep: 2 × 8 × 4 × 1 = 64 cu ft, with 10 percent allowance 70.4 cu ft or 2.61 cubic yards, which is 47 bags of 1.5 cu ft.

Settling, density and bag sizes

Soil settles after it is placed and watered. Iowa State University Extension notes that soil in a new raised bed often settles and suggests leaving room at the top for mulch; it gives no percentage. The allowance of 10 percent in the form is an example of this site, not a rule. Miracle-Gro states that 2 bags of its 1.5 cu ft raised bed soil fill a 2 × 2 ft bed 6 in deep, which is 2 cu ft of space, so follow the fill guidance on your bag where there is one.

The metric bulk density of 1400 kg per m³ is the figure Australian Native Landscapes states for topsoil. The US example of 87 lb per cu ft is the same figure converted, because we did not find a US source for topsoil alone. Bag examples: a 750 L bulk bag (Rolawn, UK), 0.75 cu ft bags of topsoil (Scotts) and 1.5 cu ft bags of raised bed soil (Miracle-Gro).

Common mistakes

• Measuring the outside of a raised bed. The soil fills the inside, which is smaller by the thickness of the boards on both sides.
• Entering the depth in feet or metres instead of inches or millimetres.
• Buying exactly the volume of the bed. Soil settles, and a bed that is filled to the top the first day will be lower later.
• Using the weight for a bagged mix. Bags are sold by volume; the weight matters only for bulk deliveries and trailers.
• Forgetting that a bulk bag may hold less than a cubic metre. Ask for its volume.