Compost Calculator
Soil & OrganicMeasurements in, purchasing amount out
How the Compost Calculator works
The calculator finds volume first, then applies the selected material’s estimated bulk-density range to show weight. Your suggested order adds 10% for settling, uneven ground, and small measurement errors.
Using your measurements
12 ft × 8 ft × (2 in ÷ 12) ÷ 27 = 0.59 cu yd
Density assumption: Finished screened compost · 800–1,200 lb/yd³
The full breakdown
How much compost a lawn, bed, or pot actually takes
The volume math above is exact, but compost is where the amount people search for actually differs by job: a lawn gets topdressed in a thin layer measured in fractions of an inch, a garden bed gets compost worked into the top several inches, and a raised bed gets compost blended through the whole fill. Pick the shape and depth that matches what you’re actually doing rather than one generic run, and the calculator handles cubic yards, cubic feet, or litres if you flip the metric toggle.
Compost also has the widest weight range of anything on this site, because moisture dominates it more than any other material here. The same cubic yard of finished compost can run close to 800 lb dry and past 1,600 lb soaked through, so the weight figure below is deliberately a range rather than a single number — useful for planning a delivery’s load limit, not for an invoice.
If you’re producing your own rather than buying it, the volume side of this calculator still tells you how much finished compost a given bin or pile needs to yield to fill your beds — useful for sizing a compost bin, or for deciding whether a backyard pile can realistically keep up with a vegetable garden’s yearly needs.
Compost type changes the weight, not the volume
Cubic yards or litres needed stay the same regardless of compost type — only the weight estimate moves. Leaf mold and screened finished compost sit toward the light end; mushroom compost and wet or dense compost run heavier, and manure-based compost can run heavier still depending on bedding content.
| Compost | Weight |
|---|---|
| Leaf mold | 600–1,000 lb/yd³ |
| Mushroom compost | 900–1,300 lb/yd³ |
| Wet or dense compost | 1,200–1,600 lb/yd³ |
| Composted manure | 1,000–1,400 lb/yd³ |
How much compost, and how deep
Depth, or blend ratio, is a job decision, not a universal number. These are common starting points for the situations people search for most.
| Topdressing an existing lawn | 1/4–1/2 in (0.5–1 cm), 1–2×/year |
|---|---|
| Amending an existing garden bed | 2–3 in worked into the top 6 in |
| Filling a new raised bed, blended with soil | 25–50% of the bed’s total volume |
| Container or potting mix amendment | 10–20% of the pot’s total volume |
Bagged, bulk, or homemade
Bagged compost suits containers and small beds; bulk delivery is cheaper per yard once a project needs more than two or three cubic yards, and it’s the only practical option for topdressing a full lawn. A home compost bin or tumbler is the third option — a basic bin typically runs $30–$100 and a tumbler $100–$300, and either one can supply a few raised beds a year once established, though rarely enough for a whole lawn topdressing.
- 27 × 1 cu ft bags ≈ 1 cubic yard
- 18 × 1.5 cu ft bags ≈ 1 cubic yard
- 13.5 × 2 cu ft bags ≈ 1 cubic yard
A standard pallet holds roughly 60–70 bags of 1-cubic-foot compost, though exact counts vary by retailer and bag size.
Two ways compost underperforms
Using unfinished compost
Compost that still smells sour, feels hot in the middle, or has recognizable scraps in it hasn’t finished breaking down. Digging it into soil at that stage can tie up nitrogen and stress plant roots — finished compost is dark, crumbly, and smells like earth, not like the bin it came from.
Piling it on instead of working it in
A thick layer of compost left on the surface acts more like mulch than an amendment — it feeds soil life slowly from the top down instead of improving the root zone directly. On an existing bed, work compost into the top several inches rather than piling it deep on top.
Compost, specifically
Compost questions people actually ask
Why add 10% to the calculated amount?
Extra material covers small dips, settling, spillage, and measurements that are not perfectly square. The calculated amount remains visible so you can compare both figures.
Are bag counts based on the same amount?
Both are shown. “Calculated” bags cover the measured volume; “Order” bags include the 10% allowance and round partial bags up to whole bags.
How accurate is the weight estimate?
Volume comes directly from your dimensions. Weight is a range because moisture, particle size, composition, and compaction change bulk density.
What is compost?
Decomposed organic matter — food scraps, yard waste, and other plant material broken down by microbes into a dark, crumbly, soil-like material used to improve soil structure, moisture retention, and nutrient content. Finished, organic compost is often what gardeners mean by “compost soil.”
How do you compost?
Alternate carbon-rich “browns” (dry leaves, cardboard, straw) with nitrogen-rich “greens” (food scraps, grass clippings) at roughly a 2-to-1 or 3-to-1 ratio by volume, keep the pile about as damp as a wrung-out sponge, and turn it every few weeks to add oxygen. Finished compost typically takes two to six months depending on how often it’s turned.
How do you make a compost bin?
A basic bin can be built from a plastic storage tote with drilled airflow holes, a welded-wire cylinder, or stacked wooden pallets. It needs enough volume to hold heat — at least about one cubic yard — plus airflow gaps and, ideally, contact with bare ground so worms and soil organisms can get in.
How do you make mushroom compost and use it?
Mushroom compost is a byproduct of commercial mushroom farming — typically straw, manure, and gypsum that’s already been used to grow a mushroom crop — rather than something composted at home from scratch. It arrives finished and is spread as a soil amendment or mulch, though it can carry more soluble salts than regular compost, so it’s often used more sparingly around salt-sensitive plants.
What is the difference between mushroom compost and regular compost?
Mushroom compost is the spent growing medium from mushroom farms — mostly straw, manure, and gypsum — so it arrives finished, fairly uniform, and often a little heavier per yard than leaf or yard-waste compost. It usually carries more soluble salts and a higher pH, which suits lawns and most vegetable beds but not acid-loving plants such as blueberries, azaleas, and rhododendrons, or young seedlings. Regular compost varies more from batch to batch but is gentler. Pick mushroom compost in the calculator above to use its own weight range.
What can and cannot go in a compost pile?
Fruit and vegetable scraps, coffee grounds, eggshells, yard trimmings, and plain cardboard or paper all compost well. Avoid meat, dairy, oily food waste, diseased plants, pet waste, and treated wood, which attract pests, smell, or introduce pathogens the pile can’t reliably kill.
How do you use finished compost in your garden?
Work it into the top several inches of an existing bed, blend it through a raised bed’s fill at roughly a quarter to half of the total volume, or spread a thin topdressing layer on an established lawn. It’s an amendment, not a growing medium on its own, so pair it with soil rather than planting into pure compost.
How much does a compost bin cost?
A basic plastic or wire bin typically runs $30–$100; a rotating tumbler bin runs roughly $100–$300 depending on capacity; and a bin built from pallets or scrap material can cost close to nothing beyond the materials on hand.
How do you make a compost pile?
Choose a level spot with some drainage, layer browns and greens as they become available, keep the pile moist but not soggy, and turn it every few weeks to keep oxygen moving through it. A pile at least one cubic yard in size holds heat far better than a small one, which speeds decomposition.