How much topsoil do I need?

When to stop buying bags

Topsoil volume is the same calculation as any other loose material: length times width times depth, with the depth converted from inches to feet, then divided by 27 to get cubic yards. A 20 by 10 foot bed filled 6 inches deep comes to 100 cubic feet, which is 3.7 cubic yards.

The number worth paying attention to is the bag count. A 40 lb bag of topsoil holds about 0.75 cubic feet, so that same bed needs 134 bags. At typical prices that is several times the cost of a bulk delivery, and it means loading and unloading 134 bags by hand. The crossover point is around one cubic yard: below that, bags are more convenient; above it, order bulk and have it dumped.

Weight matters if you are hauling it yourself. Screened topsoil runs roughly 1.1 short tons per cubic yard when dry, so 3.7 yards is about 4 tons — well beyond what a half-ton pickup should carry in one trip. Wet soil is considerably heavier, and suppliers sell by weight after rain just as they do before it.

For depth: a new planting bed wants 4 to 6 inches of good soil, vegetable beds want 8 to 12, and topdressing an existing lawn takes only a quarter to half an inch at a time. Filling deeper than the plants need is the most common way people overspend here.

A worked example: three raised beds

Three raised beds, each 8 feet long, 4 feet wide and 12 inches deep, are a common first garden. Each bed holds 8 × 4 × 1 = 32 cubic feet, so the three together need 96 cubic feet, or 3.56 cubic yards. In 40 lb bags of 0.75 ft³, that is 128 bags.

That bag count is the reason most people order bulk for raised beds. It is also worth knowing that raised beds are usually not filled with topsoil alone: a common mix is about 60% screened topsoil and 40% compost, which drains better and feeds the plants. Use the calculator for the total volume, then split it between the two materials.

How much topsoil per 100 square feet

Mistakes that cost money

• Buying fill dirt for planting. Fill dirt is subsoil for leveling and backfill; it has little organic matter and plants struggle in it. For beds and lawns, ask for screened topsoil.
• Not allowing for settling. Loose topsoil settles as it is watered in, often by 10 to 20%. For raised beds, fill to the top and expect to add a little the following season.
• Dumping the load on the lawn after rain. A loaded dump truck on wet turf leaves ruts that are harder to fix than the job you ordered the soil for. Have it dropped on the driveway on a tarp, or wait for dry ground.
• Skipping a soil test. A basic test costs little through most state extension services and tells you whether the soil you are adding, or the soil you already have, needs lime or sulfur.

What it costs

Bagged topsoil generally costs $2 to $5 per 40 lb bag in the US. Screened bulk topsoil usually runs $20 to $50 per cubic yard before delivery, and premium blends with compost cost more. For the raised beds above, 128 bags would cost roughly $256 to $640, against about $70 to $180 for 3.5 yards of bulk plus delivery. Local prices vary widely, so call two suppliers before ordering.