How the volume and weight are worked out
The area is treated as a rectangle: length multiplied by width multiplied by depth, with the depth converted to the same unit as the length first. That gives the volume in cubic yards.
Weight is the volume multiplied by the density, which for topsoil is 80 lb per cubic foot. Loose material is less dense than the same material compacted, so this figure matches what a supplier loads rather than what it becomes in place.
The bag or bulk bag count is the weight divided by the pack size and rounded up, because you cannot buy part of a bag.
Worked example
A border 12 feet by 6 feet at 6 inches is 36 cubic feet, or 1.33 cubic yards. At 80 lb per cubic foot that is 1.46 short tons, which is 72 bags of 0.5 cubic feet.
Change any input and all three outputs move together. The count always rounds up, so a job that needs 2.1 bulk bags is quoted as 3.
Why soil is ordered by volume, not weight
Topsoil is sold by the litre or the cubic metre in bags and by the cubic yard loose, because its weight depends on how wet it is. Dry topsoil is around 1,300 kg per cubic metre; wet soil can be half as heavy again.
Freshly tipped soil settles by roughly 10 to 15 per cent, so a bed filled to the brim will drop below the edging after a few weeks of watering. Add that allowance if the finished level matters.
The quality of topsoil varies far more than its quantity. A screened loam with organic matter behaves very differently from subsoil sold as topsoil, and no calculator can tell them apart.
Limits of this calculator
It assumes a flat rectangular area at one depth. It does not account for a slope, a curved edge or a trench, all of which need the area measured separately.
It uses a typical loose density of 80 lb per cubic foot. Suppliers vary, and damp material weighs more, so treat the weight as an estimate and the volume as the figure to order on.
It does not include a price, delivery, a crane charge or waste from spillage. Add your own percentage if the site is awkward.
For a decorative surface layer rather than a base, use the US gravel calculator.
Inputs for the US topsoil calculator
Length
The long side of the area, in feet.
Width
The short side of the same area, in feet.
Depth
The layer thickness in inches, which is the finished depth, not the loose depth.
CALCULATOR QUESTIONS
US soil calculator questions
How much does a cubic yard of topsoil weigh?
About 80 lb per cubic foot. The exact figure depends on moisture and grading, which is why suppliers quote a range.
Should I order extra?
Add 5 to 10 per cent for an irregular shape or an uneven base. For a simple rectangle at a constant depth, the calculated figure is enough.
Is the depth the loose or the finished depth?
Enter the finished depth. If the material compacts, the loose layer you lay will be thicker than the number you enter.
Does this work for a a border, lawn or raised bed?
It works for any flat area. For a a border, lawn or raised bed it gives the quantity; it does not specify the material grade, which your supplier should confirm.