How to measure
Use these guides to identify the measurements the calculator needs. Drawings are not to scale.
Triangle: A is the base; B is height at a right angle to that base, not the sloped side.
Circle: D is the diameter through the center, not the radius.
Check the unit beside every field. For example, 10 ft 6 in is 10.5 ft. A layer depth may use inches while length uses feet.
Work out the layer you need to add
Enter the area and the depth of new soil, not the total depth of an existing bed. Choose a rectangle, circle, or triangle, or enter an area you already know. The result works for an even layer; for uneven ground, divide it into smaller areas with their own average depths.
A 10 × 10 ft area with 3 inches of new topsoil takes 25 cubic feet before extra. At the initial 10% allowance, that is 27.5 cubic feet, about 1.02 cubic yards, or 28 one-cubic-foot bags.
How it works
Volume = area × depth. In US units, depth in inches is divided by 12 to get feet. Divide cubic feet by 27 for cubic yards. The extra percentage is applied to volume, and the bag count is rounded up after dividing by your bag’s capacity.
Changing to metric converts your existing measurements. Metric bag volume is entered in liters: 1,000 liters equals one cubic meter. A 2 × 3 m bed receiving 10 cm of soil needs 0.6 m³ before extra. With 10% extra, that is 660 liters or 17 bags of 40 liters.
Topsoil, fill, and raised beds
This is a volume calculation, not a soil specification. Topsoil, fill dirt, compost, and raised-bed blends can have different uses and settling behavior. The calculator does not choose the mix or estimate nutrient requirements.
Weight is deliberately omitted. A cubic yard does not have one dependable weight across wet, dry, sandy, and organic soils. If your supplier sells by weight, ask them to convert the estimated volume using their product’s bulk density. The extra field is an adjustable assumption, initially 10%, not a prediction of settlement.