Compost Calculator
A compost calculator multiplies area by depth to find how much compost to buy. Pick your project, enter the size, and read cubic feet, cubic yards, bags and weight. A 10 by 5 foot garden bed at 2 inches needs 8.33 cubic feet, which is 0.31 cubic yards or nine 1-cubic-foot bags.
This tool is part of our volume calculators. Use it to size an order. Check the bag label and your supplier's bulk density before you buy.
- Updated October 2026
- Sources Cited
- No Login Required
- Free to Use
Your compost
Compost to buy
0.31 cu yd
8.33 cu ft, or 9 bags of 1 cu ft
- Area
- 50 sq ft
- Cubic feet
- 8.33
- Cubic yards
- 0.309
- Cubic meters
- 0.236
- Bags (1 cu ft)
- 9
- Weight
- 309 lb (0.15 tons)
Across the cited range for this project: 4.17 to 8.33 cu ft, or 0.15 to 0.31 cu yd (5 to 9 bags).
Mix check
25% compost is within the 25 percent guide for a soil blend.
Weight uses your bulk density. Wet compost weighs more.
Cited depth ranges
Low and high quantity for each project, with the source.
Mix check
Flags a blend above the 25 to 30 percent compost cap.
Bags and weight
Pick your bag size and bulk density for a closer order.
Estimates are for material planning. Depth advice differs by plant, soil and local conditions. Check your supplier's product sheet.
How to calculate how much compost you need
Multiply the area in square feet by the depth in inches, then divide by 12 to get cubic feet. Divide cubic feet by 27 for cubic yards. Divide cubic feet by the bag size and round up for bags. A 100 square foot bed at 1 inch needs 8.33 cubic feet.
- Measure each area in feet. For a round bed, measure the diameter and use pi times the radius squared.
- Pick the depth for your project from the table below.
- Cubic feet equal area times depth in inches, divided by 12.
- Cubic yards equal cubic feet divided by 27.
- Bags equal cubic feet divided by the bag size, rounded up.
If you only know the room or yard in other units, find the area with our square footage calculator. For a total delivery of several materials, add the volumes with the cubic yards calculator.
How deep to spread compost by project
Extension and industry sources agree on thin layers. Lawns take 1/4 to 1/2 inch. Compost mixed into soil is 1 to 2 inches, worked 6 to 8 inches deep. Compost used as a mulch is 2 to 3 inches thick. The table lists each range with its source.
| Project | Depth or share | Note | Source |
|---|---|---|---|
| Lawn topdressing | 1/4 to 1/2 in | Once or twice a year | Composting Council, UF/IFAS, McGill |
| New lawn or garden, mixed into soil | 1 to 2 in, mixed 6 to 8 in deep | Share of the blend is depth divided by mix depth | Composting Council, McGill |
| Garden, before planting | 2 to 4 in mixed into soil | Improves structure and drainage | UF/IFAS, June 2026 |
| Flower beds, trees and shrubs | 1 to 2 in | Keep compost off plant crowns | Composting Council |
| Compost as a mulch layer | 2 to 3 in | Beds, trees, shrubs, vegetables | K-State MF3370 |
| New topsoil blend | 20 to 30 percent compost by volume | 70 to 80 percent subsoil | Composting Council |
| Raised beds and containers | No more than 25 percent compost | 25 to 30 percent in a soil blend | McGill Compost |
Worked example: a 10 by 5 foot garden bed
A 10 by 5 foot bed has 50 square feet. At 2 inches deep, that is 8.33 cubic feet, or 0.309 cubic yards. In 1-cubic-foot bags, the bed needs 9. Mixed into the top 8 inches of soil, the compost is 25 percent of the blend. At 1,000 pounds per cubic yard, it weighs about 309 pounds.
| Case | Area, sq ft | Depth, in | Cubic ft | Cubic yd | Bags | Weight, lb |
|---|---|---|---|---|---|---|
| 10 x 5 ft garden bed, mixed in | 50 | 2 | 8.33 | 0.309 | 9 | 309 |
| 10 x 10 ft bed, mixed in | 100 | 1 | 8.33 | 0.309 | 9 | 309 |
| 20 x 10 ft bed, compost mulch | 200 | 3 | 50.00 | 1.852 | 50 | 1,852 |
| 1,000 sq ft lawn, low | 1,000 | 0.25 | 20.83 | 0.772 | 21 | 772 |
| 1,000 sq ft lawn, high | 1,000 | 0.5 | 41.67 | 1.543 | 42 | 1,543 |
| 110 x 80 ft lawn, high | 8,800 | 0.5 | 366.67 | 13.580 | 367 | 13,580 |
How much compost for 1,000 square feet
A lawn topdressing of 1/4 to 1/2 inch needs 20.83 to 41.67 cubic feet per 1,000 square feet. That is 0.77 to 1.54 cubic yards. A bed mixed 1 to 2 inches deep needs 83.33 to 166.67 cubic feet per 1,000 square feet.
| Project | Cubic ft | Cubic yd | 1 cu ft bags |
|---|---|---|---|
| Lawn, 1/4 in | 20.83 | 0.77 | 21 |
| Lawn, 1/2 in | 41.67 | 1.54 | 42 |
| Bed mixed in, 1 in | 83.33 | 3.09 | 84 |
| Bed mixed in, 2 in | 166.67 | 6.17 | 167 |
Buy a lawn order by the yard when it passes a few cubic yards, because 27 bags of 1 cubic foot equal one yard. Ask your supplier for the bulk price and delivery fee.
Compost for raised beds and soil blends
McGill Compost advises no more than 25 percent compost in containers or raised beds, and 25 to 30 percent in a soil blend. A 4 by 8 foot bed 11 inches deep holds 29.33 cubic feet. At 25 percent, the bed needs 7.33 cubic feet of compost, or 8 bags of 1 cubic foot.
| Raised bed | Total fill, cu ft | Compost at 25%, cu ft | Compost at 30%, cu ft | Bags at 25% | Cu yd at 25% |
|---|---|---|---|---|---|
| 4 x 8 ft, 11 in deep | 29.33 | 7.33 | 8.80 | 8 | 0.272 |
| 4 x 8 ft, 12 in deep | 32.00 | 8.00 | 9.60 | 8 | 0.296 |
The rest of the fill is topsoil and other material. Size it with the topsoil calculator. For compost worked into existing soil, the share equals compost depth divided by mix depth.
| Compost depth | Mix depth | Share of blend | Mix check |
|---|---|---|---|
| 1 in | 8 in | 12.5% | Within the 25 percent guide |
| 2 in | 8 in | 25% | Within the 25 percent guide |
| 2 in | 6 in | 33.3% | Above 30 percent |
| 3 in | 6 in | 50% | Above 30 percent |
How much does a bag or a yard of compost cover?
One cubic foot of compost covers 12 square feet at 1 inch deep. One cubic yard covers 324 square feet at 1 inch. At 1/2 inch, a yard covers 648 square feet. Check the label for the bag volume, because a 40 pound bag is not always 1 cubic foot.
| Depth | Sq ft per 1 cu ft | Sq ft per cu yd |
|---|---|---|
| 0.25 in | 48 | 1,296 |
| 0.5 in | 24 | 648 |
| 1 in | 12 | 324 |
| 2 in | 6 | 162 |
| 3 in | 4 | 108 |
How much does compost weigh?
Oregon State Extension gives about 1,000 pounds per cubic yard for screened compost at 50 percent moisture. As-is values run from 800 to more than 1,600 pounds per cubic yard. A 10 by 5 foot bed at 2 inches is 0.309 cubic yards, or about 309 pounds at 1,000.
| Bulk density | 1 cu yd, lb | 1 cu ft, lb | Example bed, lb |
|---|---|---|---|
| 800 lb per cu yd | 800 | 29.6 | 247 |
| 1,000 lb per cu yd | 1,000 | 37 | 309 |
| 1,600 lb per cu yd | 1,600 | 59.3 | 494 |
Convert between cubic feet and cubic yards with the cubic feet calculator. Wet compost is heavier, so use a higher density for a rain-soaked pile.
What this calculator does not cover
This page sizes a compost order. It does not plan a compost pile or a carbon to nitrogen recipe. It shows no prices unless you enter them, because this run had no sourced unit costs. It gives no settling factor for compost.
For a surface cover of wood chips or bark, use the mulch calculator. For new turf, plan the roll count with the sod calculator. Inputs are in feet and inches. Metric input is not built yet.
Methodology and sources
Published October 2026. Last updated October 2026. Next review October 2027.
Reviews: project calculators · 31 calculators reviewed
Marcus Johnson is a Certified Construction Manager (CCM) with 20 years of experience in residential and commercial site work. He holds CCM certification from CMAA (member #2019-1247). He has managed NALP-member landscape installation projects covering more than 2 million square feet of site work. At CalcSummit, he writes all landscape volume and bulk-material calculators, applying field-tested coverage rates for mulch, gravel, sand, topsoil, and fill dirt.
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