Soil Calculator
Calculate soil volume from length, width, and depth with unit conversions. See cubic feet and yards so you can order soil with confidence.
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What the soil calculator does
Filling a bed or levelling a patch of ground takes more soil than it looks, and soil is awkward to return once it is tipped in your driveway. So it pays to get the amount right first. This works it out. You give it the length, width, and depth of the area, and it returns the volume in cubic yards and cubic feet, plus how many standard bags that comes to.
Below is how it gets there, the depths that suit different planting, and whether to buy in bulk or in bags.
How to use it
- Enter the length and width. The footprint of the bed or area, each with its own unit.
- Enter the depth. How deep you want the soil to sit.
- Press Calculate for the volume and bag count, or Reset to clear it.
How the volume and bags are worked out
The volume is simply the area times the depth:
Volume = length × width × depth
The calculator works that out in cubic feet, then divides by 27 to give cubic yards as well, since bulk soil is sold by the yard. For the bag count it assumes a common 0.75 cubic foot bag, the size most bagged soil comes in, and rounds up to whole bags. That gives you both numbers: the yardage to order in bulk, and the bags to grab if you are buying from a garden centre.
How deep your soil should be
The depth is the number that decides the whole order, and the right one depends on what you are growing. Refreshing or topping up an existing bed usually wants 3 to 6 inches. A new raised bed is deeper, often 6 to 12 inches, and root crops like carrots and potatoes want the deeper end so the roots have room.
One thing worth allowing for: soil settles after it is laid and watered, dropping a little from its loose depth. So it is sensible to be slightly generous with the depth rather than measure it tight.
A worked example: a raised bed
Say you are filling a raised bed 8 feet long, 4 feet wide, and 10 inches deep.
The volume is 8 × 4 × 0.83 = about 26.7 cubic feet, which is just under 1 cubic yard. In bags, that is roughly 36 bags at 0.75 cubic feet each.
That is a tidy example of why the two numbers matter: a yard delivered in bulk is one decision, while 36 bags is a lot of trips from the car, so the size of the job often decides how you buy it.
Soil, topsoil, and dirt
The words get used loosely, but they are not quite the same thing. Topsoil is soil that has been screened, run through a sieve to take out the stones, roots, and clumps, so it is even and easy to work. Plain dirt is the raw stuff, fine for filling and grading but without the screening. For visible beds and planting you usually want screened topsoil, and for bringing up a low area, cheaper fill dirt does the job.
The volume you need is the same whichever you pick. It is only the price, the texture, and what you can grow in it that change.
Bulk or bags
Bags suit small jobs, a single bed or a few pots, where they are easy to carry and store and you only buy what you need. Bulk soil, delivered by the yard, is cheaper per unit and far less lifting for a big project, as long as you have somewhere for the pile to land.
Either way, add a little to the figure for settling, and round up. A bed that comes up a couple of inches short after watering is a small but annoying thing to fix later.
Questions people ask
How much soil do I need?
Multiply the length, width, and depth for the volume. An 8 by 4 foot bed at 10 inches deep needs just under a cubic yard, or about 36 standard bags.
How many bags of soil are in a cubic yard?
About 36, if the bags hold 0.75 cubic feet each, since a cubic yard is 27 cubic feet.
How deep should soil be in a raised bed?
Usually 6 to 12 inches, going deeper for root crops that need the room. Topping up an existing bed needs less, around 3 to 6 inches.
What is the difference between topsoil and dirt?
Topsoil is screened to remove stones and clumps, so it is even and good for planting. Plain dirt is unscreened, better suited to filling and grading.
References
A quick note on the numbers. The volume is pure geometry, the area times the depth, with 27 cubic feet making up a cubic yard. The bag count assumes a common 0.75 cubic foot bag, the usual retail size for bagged soil. The unit conversions follow the US National Institute of Standards and Technology guide.
- National Institute of Standards and Technology (NIST), Special Publication 811, Guide for the Use of the International System of Units (SI). https://www.nist.gov/pml/special-publication-811
Mahendra Thapaliya is a graduate student in Structural Engineering at the University of Bologna, with research interests in structural systems, FEM, earthquake engineering, and numerical modeling. At Eon Tools, he reviews construction tools.