Compost Calculator
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How much compost to buy for a lawn, raised bed or pot, plus your browns to greens and carbon to nitrogen ratios.
Quick answer: To work out how much compost you need, multiply the area by the depth. For a lawn at the 1/4 inch that Virginia Cooperative Extension recommends, 1,000 square feet needs 0.77 cubic yards. For a 4x8 raised bed filled 10 inches deep, compost at a 30% share is 8 cubic feet, about 0.30 cubic yards. Use the tabs below for volume, bags, cost and weight in feet or meters, or to check a pile's browns to greens ratio.
Enter each material's mass, its carbon and nitrogen as percentages of dry weight, and its moisture. Use any one mass unit.
Material 1
Material 2
Material 3 (optional)
Compost needed
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📐 Formula
Volume = area x depth. In feet and inches: cubic feet = square feet x inches / 12, and cubic yards = cubic feet / 27. In meters: cubic meters = square meters x centimeters / 100, and liters = cubic meters x 1,000. A round pot has area = pi x diameter squared / 4. For bed fill, compost = soil volume x its share (30% if blank). Browns to greens = browns / greens. Carbon to nitrogen (Cornell) = sum of (mass x (1 - moisture) x carbon %) / sum of (mass x (1 - moisture) x nitrogen %).
How to Use the Compost Calculator
Choose a mode
Use the first tab to work out how much compost to buy, the second to check a browns to greens ratio, and the third to work out a carbon to nitrogen ratio by weight.
Pick the use and the units
For the first tab, choose lawn top-dressing, bed or pot fill, or a custom depth, then feet and inches or meters and centimeters. Pick rectangle or round.
Enter the size and depth
Type the length and width, or the diameter for a round pot, then the depth. Lawn top-dressing uses 1/4 inch if you leave depth blank, and bed fill uses a 30% compost share if you leave that blank.
Add bag size and prices if you want them
Bag size, price per bag and a bulk price are optional. They give a bag count and costs in your own currency.
Read the result
See the volume, bags, cost and weight. On the other tabs, see the ratio and what to add to bring it into range.
What is a compost calculator?
Searches for a compost calculator mean two different jobs. One is working out how much compost to buy or spread: for a lawn, a vegetable bed, a raised bed or a pot. The other is balancing a compost pile, so that browns and greens, or carbon and nitrogen, are in the right proportions. This page does both. The first tab works out volume, bags, cost and weight in feet and inches or in meters and centimeters. The second tab checks a browns to greens ratio by volume. The third tab works out a carbon to nitrogen ratio by weight with the method Cornell Composting publishes.
How much compost do I need?
The volume is the area times the depth. In feet and inches, multiply the area in square feet by the depth in inches, divide by 12 for cubic feet, then divide by 27 for cubic yards. Virginia Cooperative Extension gives the shortcut for a lawn: area in square feet times depth in inches times 0.0031 equals cubic yards. In metric, a layer one millimeter deep over one square meter is one liter, so the depth in millimeters is the liters per square meter. The table shows both, worked out from those rules.
| Depth | Per 100 sq ft | Per 1,000 sq ft | Per square meter |
|---|---|---|---|
| 0.25 in | 2.1 cu ft | 0.77 cu yd | 6 liters (0.6 cm) |
| 0.5 in | 4.2 cu ft | 1.54 cu yd | 13 liters (1.3 cm) |
| 1 in | 8.3 cu ft | 3.09 cu yd | 25 liters (2.5 cm) |
| 2 in | 16.7 cu ft | 6.17 cu yd | 51 liters (5.1 cm) |
| 3 in | 25.0 cu ft | 9.26 cu yd | 76 liters (7.6 cm) |
| 4 in | 33.3 cu ft | 12.35 cu yd | 102 liters (10.2 cm) |
How deep to spread depends on the job. Virginia Cooperative Extension recommends spreading compost on a lawn about a quarter inch thick, and warns that a thicker layer can smother the grass. For a new bed where you dig compost into the soil, the amount is usually given as a share of the mix rather than a depth, and the next section covers that share.
How much compost for a raised bed?
For a raised bed, work out the soil volume first, then take the compost share of it. Penn State Extension recommends a mix of 70% soil and 30% compost for raised beds, and Iowa State Extension gives roughly 70% topsoil and 30% compost as one option. The calculator uses 30% unless you enter another figure. Compost is not the only ingredient, so the share also tells you how much topsoil to buy.
Worked example: how much compost for a 4x8 raised bed
A 4 ft by 8 ft bed filled 10 inches deep holds 4 x 8 x 10 / 12 = 26.7 cubic feet of mix. At 30% compost that is 8.0 cubic feet of compost, which is 0.30 cubic yards or eight 1 cubic foot bags. At about 1,000 pounds per cubic yard, the compost weighs close to 300 pounds. The other 18.7 cubic feet is topsoil and any other ingredient. Choose "Bed, planter or pot fill", enter 4 and 8 for length and width and 10 for depth, and the calculator returns the same figures.
| Bed size | Soil volume | Compost at 30% |
|---|---|---|
| 4 x 4 ft | 13.3 cu ft | 4.0 cu ft (0.15 cu yd) |
| 3 x 6 ft | 15.0 cu ft | 4.5 cu ft (0.17 cu yd) |
| 4 x 8 ft | 26.7 cu ft | 8.0 cu ft (0.30 cu yd) |
| 4 x 12 ft | 40.0 cu ft | 12.0 cu ft (0.44 cu yd) |
| 8 x 8 ft | 53.3 cu ft | 16.0 cu ft (0.59 cu yd) |
How much compost for a lawn: top dressing and overseeding
Top dressing is a thin layer of fine compost raked into the lawn. At the quarter inch that Virginia Cooperative Extension recommends, a 1,000 square foot lawn needs 20.8 cubic feet, or 0.77 cubic yards. In metric, a quarter inch is about 6 mm, so each square meter needs about 6 liters. Use fine-textured, finished compost and rake it in until little of it shows on the surface. When you are covering sown lawn seed, University of Maryland Extension gives only about 1/4 to 1/2 inch of finished compost or topsoil, so the seed is not buried; the same page caps compost or straw at about 1/4 inch, so stay near 1/4 inch with compost.
Worked example: how much compost for 1,000 square feet
A lawn 40 ft by 25 ft is 1,000 square feet. At 1/4 inch, the volume is 1,000 x 0.25 / 12 = 20.8 cubic feet. Dividing by 27 gives 0.77 cubic yards, the same as Virginia Cooperative Extension's shortcut gives (1,000 x 0.25 x 0.0031 = 0.775). At a price of 40 per cubic yard (any currency) that is about 31. For compost per square foot, a quarter inch of depth is 0.0208 cubic feet for every square foot.
How much compost for pots and containers
For a round pot, the volume is pi times the radius squared times the depth. Choose "Round" and enter the pot's diameter and depth. A 40 cm pot that is 40 cm deep holds about 50 liters, and a 50 cm pot that is 50 cm deep about 98 liters. How much of that should be compost is your call; potting mixes are usually mostly other ingredients, so the share is an input and not a fixed number. The table shows a 30% share as an example.
| Pot (diameter x depth) | Pot volume | Compost at 30% |
|---|---|---|
| 30 cm x 30 cm | 21 liters | 6 liters |
| 40 cm x 40 cm | 50 liters | 15 liters |
| 50 cm x 50 cm | 98 liters | 29 liters |
| 12 in x 12 in | 5.9 gal (US) | 1.8 gal |
| 5 gallon bucket | 5 gal | 1.5 gal |
Compost calculator in liters, cubic meters and cubic feet
Choose meters and centimeters for results in cubic meters and liters, or feet and inches for cubic feet and cubic yards. These are the conversions behind the switch.
| From | To |
|---|---|
| 1 cubic yard | 27 cubic feet = 0.765 cubic meters = 765 liters |
| 1 cubic meter | 1,000 liters = 35.3 cubic feet = 1.31 cubic yards |
| 1 cubic foot | 28.3 liters = 7.48 US gallons |
| 1 US gallon | 3.79 liters = 0.134 cubic feet |
Compost weight and bulk density
Compost is sold by volume and delivered by weight, so it helps to know both. Oregon State University Extension gives a rule of thumb: screened compost with 50% moisture has a bulk density of about 1,000 pounds per cubic yard, and it varies with moisture, particle size and compaction. The calculator uses 1,000 pounds per cubic yard (593 kg per cubic meter). A cubic yard is therefore about half a US ton. If you need the weight for a delivery, ask the supplier for theirs.
Compost ratio: browns and greens
A compost pile needs carbon and nitrogen. Browns, such as dry leaves, straw and cardboard, supply carbon. Greens, such as kitchen scraps and grass clippings, supply nitrogen. The US EPA says to add at least two to three times the volume of browns to the volume of greens. The calculator's second tab takes your volumes and says whether you meet that minimum, and how much more of which material gets you to 2.5 parts browns to 1 part greens, the middle of that two to three range. This is a rule of thumb by volume, because browns are much lighter than greens, so a small weight of browns takes up a large volume.
Compost carbon nitrogen ratio calculator (the Cornell method)
The scientific ratio is by weight. Cornell Composting gives the ideal carbon to nitrogen ratio as around 30 to 1 by weight. At lower ratios, it says, nitrogen is in excess and is lost as ammonia gas, causing odors. At higher ratios, there is not enough nitrogen for the microbes, so the compost stays cool and breaks down slowly. To work out the ratio of a mix, you need each material's mass, carbon and nitrogen as a percentage of dry weight, and moisture. The third tab does the sum with that method: the carbon in each material is its mass times its dry fraction times its carbon percentage, and likewise for nitrogen. The mix ratio is total carbon divided by total nitrogen.
| Material | Moisture | Carbon | Nitrogen | C:N (dry basis) |
|---|---|---|---|---|
| Grass clippings | 77% | 45% | 2.4% | 18.75 : 1 |
| Leaves | 35% | 50% | 0.75% | 66.67 : 1 |
Worked example: Cornell's grass and leaves
Cornell's example mixes 10 kg of grass clippings with leaves. Its moisture page asks for a 60% moisture goal and gets 6.8 kg of leaves for the 10 kg of grass, but that mix has a ratio of a little less than 37 to 1. Its C/N page uses a goal of 30 to 1 and says only 3.5 kg of leaves are needed, giving a moisture content of over 66%. Our calculator works from the rounded inputs in the table: with 3.5 kg of leaves the mix has 2.1725 kg of carbon and 0.0723 kg of nitrogen, which it shows as 30.1 to 1 with a mix moisture of 66%. Use the "Load the Cornell grass and leaves example" button on the third tab to see that result.
Compost bin size: how big should a compost bin be?
University of New Hampshire Extension says a compost pile should be a minimum of one cubic yard, and recommends a bin or pile 3 feet wide, 3 feet tall and 3 feet long. That is 27 cubic feet, or about 0.76 cubic meters. A bin smaller than that holds less heat. To see whether you have enough material, total your greens and browns in one unit such as buckets and compare the total with the 3 by 3 by 3 foot (27 cubic foot) bin. The second tab only checks the ratio.
Troubleshooting a pile that is out of balance
A pile that has gone wet and smelly needs more browns and some air. Fold in dry leaves, shredded cardboard or straw and turn the pile. A pile that is dry, cool and barely shrinking usually needs more greens and some water. Check the ratio on the second tab before adding anything, rather than guessing and guessing again over several weeks.
Using this calculator in the US, UK, Australia and Canada
Compost is sold in different units from one country to the next, so match the calculator to the label on the bag or the delivery note. In the US, bagged compost is labeled in cubic feet and bulk loads are ordered by the cubic yard, which is why the default is feet and inches. Canadian garden centers and landscape yards use both systems, so check which one your supplier quotes. UK, Australian and Canadian readers say litres and metres: in the UK and Australia, bags are labeled in litres and bulk compost is ordered by the cubic metre, so for a compost calculator in litres choose metres and centimetres and enter your bag size in litres. Prices are your own, in your currency, and bag sizes and prices vary by supplier, so the calculator asks you for yours rather than assuming them.
After the compost
Finished compost goes into beds, onto lawns and into pots. For a general count of soil, topsoil or mulch, the garden soil calculator covers beds, pots and lawns. For the fill of a raised bed, with its own lumber list, use the raised garden bed calculator. Once the bed is planted, the plant spacing calculator, the planting calendar calculator and the garden watering calculator carry on from there.
Frequently Asked Questions
Start with the job, because it sets the depth: a lawn takes a thin layer, while a bed or pot takes a share of the fill. Enter your measurements on the first tab and it returns the volume, a bag count, the cost and the weight, so you can turn the volume into an order.
The worked example above uses a bed 10 inches deep, which needs 8.0 cubic feet. Fill the same bed only 5 inches deep and the soil volume halves to 13.3 cubic feet, so compost at 30% halves to 4.0 cubic feet, four 1 cubic foot bags. Depth is the number that moves the answer most, so measure it before you shop.
One inch of compost is 0.083 cubic feet per square foot, and 2 inches is 0.167. The table above lists the amounts for the common depths.
If you think in inches, one inch is 25.4 mm, so one inch of compost is 25.4 liters per square meter. A 2 inch layer is 50.8 liters per square meter, and over 40 square meters that is 2,032 liters, or about 2.0 cubic meters.
It depends on whether you spread or fill. As a quarter inch lawn top dressing, 100 square feet needs 2.1 cubic feet. As bed fill 10 inches deep at a 30% share, a 10 by 10 foot bed needs 25.0 cubic feet. The same area gives very different answers, so pick the use in the calculator first.
Over 100 square feet, 1/4 inch is 2.1 cubic feet and 1/2 inch is 4.2. University of Maryland Extension gives only about 1/4 to 1/2 inch of finished compost or topsoil over sown seed, and another line on the same page caps compost or straw at about 1/4 inch (soil at about 1/2 inch), so with compost stay at or near 1/4 inch. Choose lawn top-dressing for 1/4 inch, or custom depth and enter 0.5 for 1/2 inch of topsoil.
If your pot is sold in gallons, remember that 1 US gallon is 0.134 cubic feet. A 5 gallon bucket at a 30% share takes 1.5 gallons of compost, about 0.2 cubic feet. Most pots taper toward the base, so measure the average diameter, or treat the result as a slight overestimate.
About 40 five-gallon buckets fill a 27 cubic foot bin, because 27 cubic feet is about 202 US gallons (27 x 7.48). Count your greens and browns in buckets, add them together, and compare the total with 40.
The two ratios measure different things. The US EPA figure, at least two to three parts of browns to one part of greens, is by volume, so you can count it in buckets. Cornell's 30 to 1 is carbon to nitrogen by weight, which allows for moisture. Use the browns and greens tab when you are counting buckets, and the carbon to nitrogen tab when you know each material's carbon and nitrogen.
Divide total carbon by total nitrogen, counting each material on its dry weight. For Cornell's 10 kg of grass at 77% moisture, the dry mass is 2.3 kg, which holds 1.035 kg of carbon at 45% and 0.0552 kg of nitrogen at 2.4%. Do the same for the leaves, add the two, and divide.
You cannot buy part of a bag, and a bed that is a little short is more annoying than one with some left over. Eight cubic feet of compost in 1.5 cubic foot bags is 5.3 bags, so the calculator shows 6, which is 9.0 cubic feet. The cost uses the whole bags, and a bulk price is shown beside it to compare.
A 10 cubic yard load weighs about 10,000 pounds, or about 5 US tons, at 1,000 pounds per cubic yard. A wetter delivery will weigh more, so ask your supplier for their weight.
Sources & Methodology
Compost application and mix figures come from named extension and agency publications. The Virginia, Maryland, Iowa State, Oregon State, EPA, New Hampshire and Cornell figures were read as text on 2026-10-04. Lawn top-dressing at about 1/4 inch and the cubic yards formula (area x depth in inches x 0.0031) are from "Composting the Lawn", a PDF from the Prince William County office of Virginia Cooperative Extension, adapted from The Weekend Gardener website. The 0.77 cubic yards per 1,000 square feet is our arithmetic from that shortcut (1,000 x 0.25 x 0.0031 = 0.775). The 1/4 to 1/2 inch of finished compost or topsoil over sown seed is from University of Maryland Extension, "Starting a New Lawn", which also says to cover seed with no more than about 1/4 inch of compost or straw, or 1/2 inch of soil. Penn State Extension's "Soil Health in Raised Beds" page could not be retrieved by automated tools on 2026-10-04, so its 70% soil and 30% compost figure is quoted from Penn State's search listing; Iowa State Extension's "What would be a good soil mix for a raised bed?" independently gives about 70% topsoil and 30% compost. The bulk density (about 1,000 pounds per cubic yard at 50% moisture) is from Oregon State University Extension EM 9217, "Interpreting Compost Analyses". The two to three parts of browns to one part of greens is from the US EPA, "Composting at Home". The minimum one cubic yard and 3 by 3 by 3 foot pile is from University of New Hampshire Extension, "Composting for the Home Gardener".
The carbon to nitrogen method, the ideal of about 30 to 1 by weight, the nitrogen-excess and high-ratio statements, and the grass and leaves example (77% and 35% moisture, 45% and 50% carbon, 2.4% and 0.75% nitrogen, 3.5 kg of leaves for a 30 to 1 goal and 6.8 kg for a 60% moisture goal) are from Cornell Composting (Cornell Waste Management Institute). Cornell states 30 to 1 as the goal and "over 66%" moisture; the 30.1 to 1 and 66% figures on this page are our calculator's output for the same inputs. Conversions between cubic yards, cubic meters, liters and gallons are exact arithmetic. The EPA gives at least two to three times as many browns as greens by volume. The heavier-on-browns bands (3 to 4 a little heavy, above 4 too many), the carbon to nitrogen bands (below 20, 20 to 25, 25 to 35, above 35) and the 2.5 to 1 target are our own estimates, not Cornell's or EPA's, and prices are whatever you enter.
- Prince William County, Virginia Cooperative Extension office: Composting the Lawn (adapted from The Weekend Gardener)
- University of Maryland Extension: Starting a New Lawn
- Penn State Extension: Soil Health in Raised Beds
- Iowa State Extension: What would be a good soil mix for a raised bed?
- Oregon State University Extension: Interpreting Compost Analyses (EM 9217)
- US EPA: Composting at Home
- University of New Hampshire Extension: Composting for the Home Gardener
- Cornell Composting: Compost Chemistry
- Cornell Composting: C/N Ratio
- Cornell Composting: Moisture Content