From area to yards to bags
The volume step is the same as any material calculation — area times depth, with depth converted to match:
Volume = length × width × depth (US: ft × ft × in ÷ 12 → ft³, then ÷ 27 → yd³)
Bags then fall out by division. The most common retail bag is nominally 40 lb, which is usually about 0.75 cubic feet of soil — 36 bags per cubic yard. The default example above, a 4 × 8 ft raised bed filled 12 inches deep, works out to 32 cubic feet: 1.19 cubic yards, or 43 bags before allowance. Seeing both numbers side by side is the point of the ledger — 43 bags through a garden gate is an afternoon; 1.2 yards from a dump truck is ten minutes and usually less money.
Raised beds: fill with a blend, not straight fill
Raised beds are the biggest reason people search for this number, and the quantity is only half the answer. Straight screened topsoil compacts in a contained bed and can drain poorly; pure compost slumps and stays too rich. The usual practice is a blend — commonly around two parts topsoil to one part compost, with plenty of variations — so run this calculator for the total volume, then split the order across components. The material selector changes the weight line, not the volume: a bed needs the same cubic feet whatever you fill it with.
Why the weight row matters
Soil is the heaviest thing most homeowners ever order. At roughly 2,000 lb per moist cubic yard — a full US ton — even a single yard exceeds the payload of a typical half-ton pickup once you add a driver and a wheelbarrow. Two yards for a modest lawn project is a small delivery truck, full stop. The weight line exists so this surprise happens on screen instead of at the landscape yard: if the figure is over about 1,000 lb, plan on delivery or multiple bagged trips rather than one heroic pickup load. Wet soil weighs noticeably more than the estimate; dry, fluffy compost noticeably less.
Lawns and topdressing
At the other extreme, lawn work uses depths measured in fractions of an inch. Topdressing an existing lawn or covering new seed takes only ¼–½ inch — the coverage table shows why a single yard stretches across 648 square feet at half an inch. Establishing a new lawn from scratch is the opposite: 4–6 inches of quality topsoil over the graded subsoil, which is where volumes (and delivery trucks) get serious. Enter the depth your project actually needs rather than a habit number; depth drives the order linearly.
Frequently asked questions
How many bags of topsoil for 100 square feet?
At 2 inches deep: 16.7 cubic feet, which is 23 bags of 0.75 cu ft. At 4 inches, double it — 45 bags — at which point bulk delivery is almost certainly the better buy.
Can I put topsoil over an existing lawn to level it?
Thin lifts only: up to about ½ inch at a time lets grass grow through. For deeper low spots, cut and lift the sod, fill underneath, and relay it — burying grass under an inch or more of soil kills it.
Do I need topsoil or fill dirt?
Fill dirt (subsoil) is for raising grade and filling deep holes — it compacts predictably and is cheaper. Topsoil is the growing layer that goes on top. Deep projects commonly use fill dirt to within a few inches of final grade, then finish with topsoil.
How much does a 40 lb bag of topsoil cover?
At about 0.75 cu ft per bag: 9 sq ft at 1 inch deep, 4.5 sq ft at 2 inches, or 3 sq ft at 3 inches.
Finishing the bed? Top it with the mulch calculator, edge or path it with the gravel calculator.