Compost Calculator
Size a compost application by rate, not by fill depth: this compost calculator gives cubic yards, cubic feet, bags and the nitrogen and phosphate the load supplies.
By CalcBuilt Editorial TeamUpdated September 9, 2026Formulas checked against manufacturer specs, see how we calculate.
Results
- Compost needed
- 1.23 cu yd
- 33.3 cu ft, from 2 in spread over 200 sq ft and worked into the top 8 in
- Compost share of the blend
- 25%
- 2 in of compost in a worked zone 8 in deep. Oregon State mixes a new landscape bed to 8 in and puts it near one third compost by volume
- 1 cu ft bags
- 34 bags
- Or 23 bags of 1.5 cu ft. One 1 cu ft bag covers 12 sq ft at 1 in deep, and 27 bags make 1 cu yd
- Nitrogen supplied
- 9.3 lb
- Total nitrogen in the load at 1.5% of dry weight. About 10% of it, or 0.93 lb, mineralizes the first season, which is 4.63 lb per 1,000 sq ft
- Phosphate supplied
- 3.1 lb
- P2O5 at 0.5% of dry weight, or 15.4 lb per 1,000 sq ft. Minnesota Extension counts all of the total phosphorus, which is what keeps soil test phosphorus from climbing
- Weight to move
- 1,235 lb
- About 1,000 lb per cubic yard fresh, 800 to 1,500 lb depending on moisture. The load is 0.62 tons
- Before you repeat this
- Take a soil test
- Compost is a soil conditioner first and a fertilizer second. Repeat applications build soil phosphorus, so test every 2 to 3 years and drop the rate when phosphorus reads high
Compost formula
Cubic feet = Area (sq ft) x Depth (in) / 12
Cubic yards = Cubic feet / 27
Compost share (%) = Depth (in) / Worked depth (in) x 100
Total N (lb) = Cubic yards x 1,000 lb x 50% solids x N (% of dry weight)
First-season N (lb) = Total N x 10%Worked example
A 200 sq ft vegetable bed getting 2 inches of compost: 200 x (2 / 12) = 33.3 cubic feet, or 1.23 cubic yards. Tilled into the top 8 inches that is 25 percent compost by volume, inside the range Oregon State and Penn State use for a new bed. At 1,000 pounds per cubic yard the load weighs about 1,235 pounds, half of it water, and at 1.5 percent nitrogen it carries 9.3 pounds of total nitrogen.
Top-dressing a 5,000 sq ft lawn at 1/4 inch: 5,000 x (0.25 / 12) = 104.2 cubic feet, or 3.86 cubic yards, which is 0.77 cubic yards per 1,000 square feet. It supplies about 29 pounds of total nitrogen, of which roughly 2.9 pounds mineralizes this season, or 0.58 pound per 1,000 square feet. That is over half of a standard 1 pound per 1,000 square feet feeding, so cut the next application.
Quick reference
| Depth | Cubic feet | Cubic yards | 1 cu ft bags | Total nitrogen |
|---|---|---|---|---|
| 1/4 in | 20.8 | 0.77 | 21 | 5.8 lb |
| 1/2 in | 41.7 | 1.54 | 42 | 11.6 lb |
| 1 in | 83.3 | 3.09 | 84 | 23.1 lb |
| 2 in | 166.7 | 6.17 | 167 | 46.3 lb |
| 3 in | 250.0 | 9.26 | 250 | 69.4 lb |
| 4 in | 333.3 | 12.35 | 334 | 92.6 lb |
A rate, not a fill depth
Compost is applied at a rate: a measured layer over an area, chosen for what it does to the soil. It is not a volume that fills a container. That is the difference between this page and a topsoil or raised bed calculator, which ask how deep the box is and multiply. Here the soil sets the number and the volume falls out of it.
Two rates cover most home work. Top-dressing an established lawn takes a quarter inch to a half inch, spread after core aeration and dragged in so it reaches the soil. Amending a bed takes 2 to 3 inches tilled into the top 6 to 8 inches, a quarter to a half of the worked zone by volume. Oregon State Extension puts a new landscape bed near one third compost by volume. Penn State tills a 1 to 2 inch layer 4 to 6 inches deep before seeding turf.
Compost counts against your fertilizer program
A cubic yard of fresh compost weighs about 1,000 pounds and is roughly half water, so it carries about 500 pounds of dry matter. At 1.5 percent nitrogen that is 7.5 pounds of total nitrogen per yard. UMass Extension measured an average of 8 pounds per cubic yard across farm composts, so the arithmetic lands where the labs do.
Most of that nitrogen is locked in organic matter. Penn State puts first-season availability at about 10 percent of the total, and UMass gives a range of 10 to 30 percent. Phosphorus behaves differently. Minnesota Extension tells gardeners to count all of the total phosphorus, because that is what keeps soil test phosphorus from climbing. Two inches of compost over 1,000 square feet supplies roughly 15 pounds of phosphate, well past the pound a starter fertilizer delivers. Several states already restrict phosphorus in lawn fertilizer without a soil test.
What this calculator leaves out
It does not read a soil test, and after the first application that is the input that should set the rate. It leaves out the analysis of your specific product and the soluble salt level that makes manure and mushroom composts risky on seed beds. Potassium, lime and pH correction, delivery fees, and the tiller or aerator rental sit outside it too. It does not check whether the compost is finished: a carbon to nitrogen ratio above 30 to 1 pulls nitrogen out of the soil instead of adding it. It also assumes an even spread, which a shovel and a rake do not give you across 5,000 square feet.
Mistakes that cost money
- Top-dressing an inch at a time instead of a quarter inch: the layer mats over the crowns and the turf roots dry out.
- Spreading 3 in on a bed and leaving it on the surface: roots stay in the compost and the compacted soil under it never improves.
- Treating compost as zero fertilizer: 2 in over 1,000 sq ft supplies about 15 lb of phosphate, more than a starter fertilizer delivers.
- Unfinished compost with a carbon to nitrogen ratio above 30 to 1 pulls nitrogen out of the soil and yellows the new planting.
- Manure or mushroom compost on a seed bed: the soluble salts cut germination, so use plant-based compost anywhere you are seeding.
- Buying bags for a yard-sized job: 27 one cubic foot bags make a cubic yard, and bulk delivery wins past about 2 yards.
Key facts
- Penn State Extension holds a compost top-dressing on established turf to about 1/4 inch per pass, because thicker layers build a surface mat that restricts rooting.
- One inch of compost over 1,000 square feet is about 3.1 cubic yards, and two inches is about 6.2 cubic yards.
- Oregon State Extension mixes a new landscape bed 6 to 8 inches deep at about one third compost by volume, which is a 2 to 2.7 inch layer.
- UMass Extension measured an average of 8 pounds of total nitrogen per cubic yard of compost, of which a little over 1 pound is available the first year.
- A cubic yard of fresh compost weighs about 1,000 pounds, and University of Minnesota Extension puts the range at 800 to 1,500 pounds depending on moisture.
Frequently asked questions
How much compost do I need for a garden bed?
Two inches over the bed, tilled into the top 6 to 8 inches. For a 200 square foot bed that is 33.3 cubic feet, or 1.23 cubic yards, about 34 one cubic foot bags. That works out to 25 percent compost by volume, the range Oregon State and Penn State use for a new bed.
How thick should compost be when top-dressing a lawn?
About a quarter inch per application. Penn State found that thicker layers left on the surface build a mat of organic matter that dries turf roots and restricts rooting into the soil below. Core aerate first, then drag the compost into the holes.
Does compost count as fertilizer?
It counts, but slowly. A cubic yard carries roughly 7 to 8 pounds of total nitrogen and only about 10 percent of that is available the first season. Phosphorus is the opposite: count all of it, because repeat applications drive soil test phosphorus high.
Can you put too much compost in a garden?
Yes. Past about a third compost by volume the bed holds water, settles as the organic matter burns off, and builds up phosphorus and soluble salts. Oregon State caps the annual top-up on an existing vegetable bed at a quarter inch to one inch.
Sources and references
- EM 9308 How to Use Compost in Gardens and Landscapes (1/4 to 1/2 in lawn top-dressing, 3 to 4 in worked into the top 8 to 12 in for new vegetable beds, about 1/3 by volume for landscape beds) (Oregon State University Extension)
- Using Composts to Improve Turf Performance (1 in equals 3.1 cu yd per 1,000 sq ft; about 10% of total N available the first season) (Penn State Extension)
- Interpreting your compost report (1,000 lb per cubic yard of fresh compost, total P counted as fully available) (University of Minnesota Extension)
- Compost Use and Soil Fertility (average 8 lb total nitrogen per cubic yard, 10 to 30% released in one growing season) (UMass Extension)
- Using Compost in Colorado Gardens (typical 1.5 to 3.5% nitrogen and 0.5 to 1% phosphate, incorporation depths by site) (Colorado State University Extension)
Next steps for this project
The usual order for a landscaping & outdoor project. See all landscaping & outdoor calculators.
Results are estimates based on standard formulas and typical product specifications. Confirm quantities with your supplier and local code before ordering.