Topsoil is what you reach for when the goal is growing — a new lawn, a raised bed, or filling and leveling before you plant.
It is sold mostly by the cubic yard in bulk, and the two things that trip people up are depth, which ranges from a paper-thin topdressing to a foot-deep raised bed, and picking the right type of soil for the job. This guide covers the formula, the depth for each project, the soil types, and the order math.
The formula
Topsoil volume is the same as any material: length x width x depth, in feet, divided by 27 for cubic yards:
- Measure length and width in feet, and convert depth from inches to feet (inches ÷ 12).
- Multiply for cubic feet, then ÷ 27 for cubic yards — the unit bulk topsoil is delivered in.
The area shortcut is (square feet x depth in inches) ÷ 324 = cubic yards. A 500 sq ft new-lawn area at 4 inches comes to 500 × 4 ÷ 324 = about 6.2 cubic yards — already firmly in bulk-delivery territory.
How deep — by the job
Depth is the decision that drives everything, and it swings widely:
- Lawn topdressing: 1/4–1/2 inch. A thin layer to fill hollows and support overseeding — more than half an inch smothers the existing grass.
- New lawn from seed: 4–6 inches of growing depth over the subsoil.
- Flower or vegetable beds: 6–8 inches worked into the existing ground.
- Raised beds: 8–12 inches — a full-depth fill across the whole footprint.
Topsoil, garden mix, compost, or fill dirt?
The volume math is identical for all of them, but they do very different jobs — buying the wrong one is the most expensive mistake here:
A simple way to remember the layering: topsoil goes under the plants; mulch goes on top of them. If you are finishing a bed, you will likely want both — see how much mulch you need for the surface layer.
Bags or bulk?
Bagged topsoil is fine for a planter, a patch, or a single small bed. But a cubic yard is roughly 36 forty-pound bags, so the moment a job passes about 1.5–2 cubic yards, bulk delivery is both cheaper and far less lifting. Bulk screened topsoil commonly runs about $30–$40 per cubic yard delivered.
Odd shapes: circles and L-shaped beds
Break any non-rectangle into simple pieces: split an L-shaped bed into rectangles, a round bed is π × radius² × depth, and a triangle is ½ × base × height × depth.
Add for settling
Order about 10% extra. Topsoil settles and compacts once it is spread and watered, and the ground beneath is never perfectly level — so the bare calculation tends to leave you a little short on finished depth.
A full worked example
A 500 sq ft new lawn at 4 inches:
- Volume: 500 × 4 ÷ 324 = about 6.2 cubic yards
- With 10% settling: order about 7 cubic yards of screened topsoil, delivered in bulk
- Spread it, rake level, then seed — bags would mean hauling roughly 250 forty-pound sacks.
Common mistakes to avoid
- Topdressing too thick — more than 1/2 inch over a live lawn smothers it.
- Using fill dirt where you meant to grow — it has little organic matter.
- Ordering bags for a bulk-sized job — the lifting and the cost both pile up.
- Forgetting settling — skip the 10% and your finished depth comes up short.
- Filling a veg bed with plain topsoil — most beds do better as a topsoil-and-compost blend.
Measure in feet, set the depth to the job, pick the right soil for what you are growing, and add 10% for settling. Bulk for anything past a yard or two, and one delivery will set you up for the season.