How Much Topsoil Do I Need? (2026 Calculator + Bag Chart)
Ordering topsoil feels like guesswork until you do the volume maths, and guessing wrong is expensive either way: too little leaves a thin, patchy bed, and too much leaves a costly pile on the driveway. This guide gives you the exact formula, a worked example, and a bag chart, plus a free calculator that does the maths for any bed size.
How much topsoil do I need?
It depends on your bed size and depth, but a typical 20 by 10 foot bed at 6 inches deep needs 3.70 cubic yards, or 50 bags of 2 cubic foot topsoil. Measure length and width in feet, choose your depth in inches, and multiply them together to get your exact volume before ordering.
The three numbers that decide everything are length, width, and depth. Measure the bed in feet, pick a depth from the guide below, and the formula does the rest. Most ordering mistakes come from guessing the depth, not from mismeasuring the bed, so settle that number first.
How many cubic yards of topsoil do I need for a 10×10 bed?
A 10 by 10 foot bed at 6 inches deep needs 1.85 cubic yards of topsoil. At 4 inches deep, the same bed needs only 1.23 cubic yards, and at 3 inches it needs 0.93 cubic yards. Depth changes the answer more than most gardeners expect, so always confirm your depth before you order.
Suppliers sell bulk topsoil by the cubic yard, and one cubic yard equals 27 cubic feet. That conversion is why small depth changes matter so much: every extra inch across a 100 square foot bed adds about 8.33 cubic feet, or roughly a third of a cubic yard, to your order.
How many bags of topsoil do I need?
Divide your cubic feet by the bag size and round up. A 20 by 10 foot bed at 6 inches deep holds 100 cubic feet, so it needs 50 bags of 2 cubic foot topsoil, 100 bags of 1 cubic foot topsoil, or 34 bags of 3 cubic foot topsoil. You cannot buy part of a bag, so round up.
Always check the bag label before you buy, because bag sizes vary. The most common garden-centre bag holds 2 cubic feet, but 1 and 1.5 cubic foot bags are also widely sold. Using the wrong bag size in your maths is the fastest way to end up a dozen bags short.
How deep should topsoil be for a new garden bed?
Six inches is the standard depth for a new flower or vegetable bed, while lawns need 4 to 6 inches and raised beds need 8 to 12 inches. A top-up of an existing bed needs only 2 to 3 inches. Going deeper gives roots more room, but it also doubles your volume and cost with every extra inch of depth.
Depth also depends on what you are planting. Shallow-rooted annuals cope with 6 inches, root vegetables and perennials appreciate 8 to 12 inches, and lawns establish best with at least 4 inches of good soil under the seed or sod. If you are levelling a lawn, apply no more than 1 to 2 inches at a time so you do not smother the grass.
Is it cheaper to buy topsoil in bags or in bulk?
Bulk topsoil is cheaper once you need more than about two cubic yards. A 20 by 10 foot bed at 6 inches deep costs about $250 in 2 cubic foot bags at $5 each, versus about $148 in bulk at $40 per cubic yard, before delivery fees. Bags win only for small beds, top-ups, and gardens a truck cannot reach.
Delivery fees can narrow the gap, so compare all-in prices. Bulk quotes often add a delivery charge, and bag prices may exclude tax. Put your real delivered prices into the Topsoil Calculator for a fair comparison, and remember that hauling 50 bags by hand is a full afternoon of work that bulk delivery skips.
Should I order extra topsoil?
Yes, order about 10% more topsoil than your calculation shows. Fresh topsoil settles when it is watered, and spillage, uneven ground, and wheelbarrow losses eat into every load. For a 20 by 10 foot bed at 6 inches, that means ordering about 4.07 cubic yards instead of 3.70, or 55 bags instead of 50.
A small surplus is cheap insurance. A thin patch caused by running short shows up as weak, uneven growth all season, while leftover soil always finds a use topping up another bed or filling a low spot. The calculator shows the exact volume, so add the 10% yourself when you order.
What kind of topsoil should I buy?
Buy screened, weed-free topsoil from a reputable supplier, and ask what the mix contains before a large bulk order. Good topsoil is dark, crumbly, and free of rubble, clay lumps, and weed seeds. Cheap fill dirt looks similar in the pile but grows poorly, and replacing it costs far more than buying quality soil once.
For garden beds, look for a loam-based mix rather than pure clay or sand. If you are also mulching the finished bed, our Mulch Calculator works out that layer separately, and the Gravel Calculator covers paths and drainage layers. For a new lawn over fresh topsoil, see the Sod Calculator.
Frequently Asked Questions
How many bags of topsoil are in a cubic yard?
One cubic yard is 27 cubic feet, so it equals 13.5 bags of 2 cubic foot topsoil, or 14 bags in practice, since you cannot buy half a bag. With 1 cubic foot bags, a cubic yard is 27 bags.
Can I use the topsoil calculator for a round bed?
For a round bed, work out its area first: multiply 3.14 by the radius in feet squared. Then use that area with your depth in the same formula, or split an irregular bed into rectangles, calculate each one, and add the volumes together.
How much does a cubic yard of topsoil cover?
One cubic yard covers 100 square feet at about 3 inches deep, 54 square feet at 6 inches deep, and 324 square feet at 1 inch deep. Deeper coverage always means a smaller area from the same load.
Disclaimer: This guide provides estimates only and is not professional landscaping advice. Real beds vary with ground level, settling, and spillage, so order about 10% extra. Prices are examples, not quotes, and vary by supplier and region.
