Topsoil Calculator

Topsoil Calculator: How Much Topsoil Do I Need?

Topsoil is sold by the cubic yard, by the ton and by the bag, but the space it has to fill is measured in feet and inches. If you are asking how much topsoil do i need, the answer depends on three things: the area you want to cover, the depth you want to reach, and how much extra you allow for the soil settling once it is watered in. This page does that maths for you in imperial or metric units, shows every formula it uses, and helps you choose between bags and a bulk delivery before you spend anything.

Whether you call it a soil calculator or a topsoil calculator, the maths is the same — this tool works out soil volumes for raised beds, new lawns and garden beds in cubic yards, cubic feet and bags.

Quick answer

For a 4 × 8 ft raised bed filled 12 inches deep, you need 0.59 cubic yards for every 4 × 4 ft section — and 1.19 cubic yards (32 cubic feet, about 22 bags of 1.5 cu ft) for the whole 4 × 8 ft bed, before any extra allowance. The table below is worked out in exactly the same way, with no extra added, so you can check every row against the formulas further down. Most people then add about 10–15% for settling — the calculator below adds that allowance for you.

Project	Depth	Cubic yards	Cubic feet	Bags of 1.5 cu ft
4 × 4 ft raised bed	12 in	0.59 yd³	16 cu ft	about 11 bags
4 × 8 ft raised bed	12 in	1.19 yd³	32 cu ft	about 22 bags
10 × 10 ft garden bed	6 in	1.85 yd³	50 cu ft	about 34 bags
Lawn topdressing, 1,000 sq ft	½ in	1.54 yd³	41.7 cu ft	about 28 bags

Check the first rows by hand: a 4 × 8 ft bed covers 32 sq ft, and at 1 ft deep that is 32 cu ft. There are 27 cu ft in one cubic yard, so 32 ÷ 27 = 1.19 yd³, and 32 ÷ 1.5 = 21.3, which rounds up to 22 bags because you cannot buy part of a bag.

The formulas

Everything on this page rests on one simple idea: topsoil fills a volume, so volume = area × depth. For a rectangle, the area is length × width. For a circle, the area is π × radius², where the radius is half the diameter. The depth has to be in the same unit as the sides, so for a rectangle measured in feet, volume in cubic feet = length (ft) × width (ft) × depth (ft), with depth in feet worked out as inches ÷ 12. An awkward shape is not a problem: split it into rectangles and circles, work out each piece, and add the volumes together.

• Cubic yards = cubic feet ÷ 27, because one cubic yard is 3 ft × 3 ft × 3 ft.
• Cubic metres = cubic feet × 0.0283 — in metric mode the same maths runs directly in metres, so area in m² × depth in metres gives m³.
• Bags = cubic feet (with extra) ÷ bag size, always rounded up, because you cannot buy part of a bag.
• Weight = cubic yards (with extra) × density. The calculator uses 1.2 tons per cubic yard unless you change it.

The settling allowance deserves its own explanation, because it is the step people most often skip. Topsoil arrives loose, full of tiny air gaps between the crumbs. Once it is spread, watered and rained on, those crumbs pack closer together, roots and worms work through it, and the surface drops — sometimes visibly within the first few weeks. That is why an extra 10–15% is standard: it is not a sales trick, it is the difference between a bed that stays level and one you have to top up almost straight away. Use about 10% for firm, well-prepared ground and closer to 15% for raised beds and soft, fluffy soil. Weight, unlike volume, is always an estimate, because density changes with the soil itself and with moisture — which is why the density box can be changed.

Worked example

Take a standard raised bed that measures 4 ft by 8 ft, to be filled 12 inches deep, at the default density of 1.2 tons per cubic yard:

• Step 1 — area: 4 ft × 8 ft = 32 sq ft.
• Step 2 — volume in cubic feet: 32 sq ft × (12 ÷ 12) ft = 32 cu ft.
• Step 3 — cubic yards: 32 ÷ 27 = 1.19 yd³.
• Step 4 — bags: 32 ÷ 1.5 = 21.3, which rounds up to about 22 bags of 1.5 cu ft.
• Step 5 — weight: 1.19 × 1.2 = about 1.42 tons (using the unrounded volume).
• Step 6 — with a 15% settling allowance: allow 15% extra on the order — about 1.37 yd³ in total, and about 26 bags if you are buying in bags instead of bulk.

Those are the numbers the calculator gives for the same inputs, so you can check any result on this page by hand. One important practical note, though: raised beds are rarely filled with topsoil alone. Pure topsoil can pack down, drain unevenly and run short of organic matter. A common mix is roughly 60% topsoil, 30% compost and 10% aeration material such as perlite, coarse grit or bark fines — or a simpler thirds mix of topsoil, compost and peat or coir. For a 60/30/10 mix, this bed needs only about 0.71 yd³ of topsoil itself (60% of 1.19 yd³), with the rest made up by compost and aeration material. The mix drains better, feeds plants sooner and settles less than topsoil on its own.

How deep should topsoil be?

The right depth depends on the job the soil has to do. Too little and roots quickly reach the poorer ground underneath; too much in one loose layer and you waste money and invite sinking. As a guide, by job:

• Lawn topdressing — ¼–½ in. A thin layer brushed down into the existing grass, levelled and watered in. More than about half an inch at once can smother the grass beneath it.
• New lawn before seeding or sod — 4–6 in. Enough depth for roots to establish, hold moisture and level out minor bumps before you seed or lay sod on top.
• Established garden beds — 6–8 in, worked into the soil below. Dig or fork the new topsoil into the existing soil rather than leaving a sharp layer, so roots and water move between the two.
• Raised beds — 12 in or more. Deeper soil suits vegetables and gives roots room, but allow for settling and fill close to the top, then top up after the first few waterings.
• Filling low spots — depth varies. Measure the deepest point and the edges and use a sensible average. Deep fills over 6 in should be compacted in layers — fill a few inches, firm it down, then repeat — so the patch does not sink again a month later.

Whatever the job, measure the depth in several places and average the readings. Ground that looks flat rarely is, and a single measurement in the middle is the most common reason an order comes up short.

Buying good topsoil

Start with the choice between screened and unscreened soil. Screened topsoil has been passed through a mesh, which removes most stones, roots and hard clumps and leaves an even texture that is easy to rake level — it costs more, and it is the sensible choice for lawns and visible beds. Unscreened topsoil is cheaper and can be perfectly good soil, but expect stones, roots and clods in it; it suits filling large low areas where the finish matters less and you can pick out the worst as you go.

Be aware that “topsoil” is a loosely regulated word — there is no single standard that a load has to meet before it can be sold under that name, and quality varies a great deal. Buy from a reputable local supplier where you can, and ask where the soil was stripped from: topsoil taken from a field or garden is a very different thing from material scraped up on a building site. Good topsoil smells earthy, looks dark and crumbly, and squeezes into a loose ball that breaks apart easily. Avoid soil that smells sour or chemical, that is full of weed seeds, stones or rubble, or that contains bits of glass, plastic or brick. Of the natural soil types, a sandy loam is the all-round ideal for most gardens: it drains freely yet still holds enough moisture and nutrients for plants, where very sandy soil dries out quickly and heavy clay drains slowly and bakes hard.

Finally, plan how the soil will actually reach you. A cubic yard of topsoil weighs about 1.2 tons, and a standard pickup bed carries roughly 1 yd³ at most — so bulk delivery suits anything over about half a yard, and saves a lot of heavy trips with bags. Bags still have their place for small jobs: they are clean, easy to store, and can be carried through a house or up steps where a delivery truck could never tip. Either way, order the settled depth you want, add the allowance, and have a barrow and a rake ready — topsoil is much easier to move once than twice.

Frequently asked questions