♻️How much compost do you need?

✓ Tested & verified Updated: Aug 6, 2026 How we calculate this

Compost calculator

Area sq ft

Depth

Bag size

Settle & waste allowance

2.8 cubic yards≈ 1.8 tons

= 76.7 cu ft · about 77 bags (1 cu ft)

Weight, dry: 3,691 lb
Loads in a half-ton pickup: 3
One cubic yard covers: 162 sq ft at this depth

Compost loses volume as it finishes breaking down — the 15% allowance covers the first season.

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How much compost do you need?

Working a 2-inch layer into a 400 sq ft bed takes 66.7 cubic feet of compost — 2.5 cubic yards, or about 2.8 yards once you allow 15 percent for settling. Area × depth ÷ 12 ÷ 27, the same as any other material.

What is different about compost is the ceiling. Two inches tilled into the top six inches of soil gives a finished profile that is 25 percent compost, which is the top of the range extension programmes recommend. Compost is an amendment: past about 30 percent by volume the bed holds too much water, slumps as decomposition finishes, and releases nitrogen faster than roots can use it.

Top dressing works to a completely different scale. A half inch across a lawn — 1.5 cubic yards per 1,000 sq ft — is a full spring feed, and anything thicker smothers the grass you were trying to help. Rake it into the sward rather than leaving it sitting on the leaf.

Compost is the one landscape material where the right answer is a thin layer applied often, not a thick layer applied once. The volume you need is therefore much smaller than for mulch or topsoil, and the depth choices are correspondingly finer — a quarter inch is a real, useful number here in a way it never is under bark.

The figures below are per 1,000 sq ft, which is roughly a small back lawn, so a typical suburban top dressing lands between one and two cubic yards.

Use	Depth	Per 1,000 sq ft	1 cu ft bags
Lawn top dressing	0.25 in	0.77 cubic yards	21
Spring feed or overseed	0.5 in	1.54 cubic yards	42
Worked into a bed	2 in	6.17 cubic yards	167
Heavy clay rebuild	3 in	9.26 cubic yards	250

Note what happens in the last column. Anything past a light top dressing is a bulk order — 167 bags is not a job anybody finishes, or wants to pay for.

Frequently asked questions

How much compost per square foot?

One inch over 100 sq ft is 8.3 cubic feet, or 0.31 cubic yards. Scale from there: 2 inches over 100 sq ft is 16.7 cubic feet, and half an inch is 4.2. In bag terms, a 1 cu ft bag covers 12 sq ft at an inch deep, which is why lawn top dressing eats bags so quickly.

How much compost should I mix into a new bed?

Two to three inches worked into the top six to eight inches of soil, which lands the compost at 25 to 30 percent of the finished volume. On heavy clay the top of that band is justified for the first two years; on soil already in good condition, one inch a year as a top dressing does more than a heavy dig ever will.

How much does a yard of compost weigh?

About 1,300 lb, in a published range of 1,000 to 1,600 lb depending on moisture and how finished it is. That makes it roughly twice the weight of shredded mulch and a little over half the weight of topsoil, so a half-ton pickup handles one yard comfortably and two only just.

Can I use compost as mulch?

You can, in a half-inch to one-inch layer, and it feeds the soil as it works in. It is a poor weed suppressant though — it is a perfect seedbed, so windblown weed seed germinates in it happily. If weed control is the point, use compost as the bottom layer and a coarse mulch on top.

How many bags of compost make a cubic yard?

Twenty-seven of the 1 cu ft bags, which is the size most compost is sold in, or 18 of the 1.5 cu ft size. At $4 to $7 a bag that is $108 to $189 a cubic yard, against $30 to $60 for bulk — the widest bagged-versus-bulk gap of any material on this site.

Is mushroom compost the same thing?

It is spent mushroom substrate — straw, manure and gypsum after a cropping cycle — and it is a good soil conditioner with one caveat: it carries more soluble salts than garden compost and can run alkaline. Keep it under 25 percent of the mix, water it in well before planting, and avoid it around acid-loving shrubs.

How we calculate this

Volume is area × depth ÷ 12 ÷ 27. One cubic yard covers 1,296 sq ft at a quarter inch, 648 sq ft at half an inch, 162 sq ft at 2 inches and 108 at 3. The settling allowance is applied on top of the calculated volume, with 15 percent as the default for compost because the organic fraction is still decomposing when it goes down. Weight uses 1,300 lb per cubic yard from our density table, the working figure inside a 1,000–1,600 lb published range. The 25–30 percent ceiling on compost as a share of finished soil volume follows university extension and US EPA guidance on using compost as an amendment rather than a growing medium.

Worked example

With Length ft 24, Width ft 15, Diameter ft 12, Base ft 20, Height ft 12, Area sq ft 400, Ring diameter ft 6, Gap around trunk (in) 4, Depth 2, Bag size 1 cu ft — Compost, garden soil, soil conditioner, Settle & waste allowance 15% — compost and raised bed mixes, this page works out 2.8 cubic yards ≈ 1.8 tons. = 76.7 cu ft · about 77 bags ( 1 cu ft )

Weight, dry3,691 lb
Loads in a half-ton pickup3
One cubic yard covers162 sq ft at this depth

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