Free compost calculator for volume, weight, and cost. Enter your area and depth to find exactly how much compost you need for your garden or lawn
- Coverage area
- 0 sq ft
- Compost volume
- 0 cu ft
- Bags needed
- 0 bags
- Bulk order
- 0 cu yd
How much compost do you need? Enter the size of your garden, lawn, or raised bed and your desired application depth, and this compost calculator instantly gives you the volume, weight, and cost — in cubic yards, cubic feet, or liters.
What is compost?
Compost is decomposed organic matter — leaves, food scraps, grass clippings, and other plant waste broken down into a dark, nutrient-rich material. Mixed into soil, it improves structure, retains moisture, and feeds the microorganisms that keep plants healthy. It's the most common low-cost way gardeners boost soil quality without switching to chemical fertilizer.
How do I calculate how much compost I need?
Compost volume is area multiplied by depth:
Volume = Length × Width × Depth
- Measure the length and width of the space (garden bed, lawn, or planting area).
- Multiply to get the area in square feet or square meters.
- Decide your application depth (see the table below), then multiply area × depth.
- Convert to cubic yards or cubic feet if you're buying in bulk, or to bag count if buying bagged compost.
Example: A 10 ft × 5 ft new garden bed with poor soil needs a heavy application, around 2 inches of compost. Area = 10 × 5 = 50 sq. ft. Volume = 50 sq. ft. × 2 in. = 8.3 cubic feet (about 0.3 cubic yards)
Example: An existing 110 ft × 80 ft lawn getting a light topdressing at ½ inch: Area = 110 × 80 = 8,800 sq. ft. Volume = 8,800 × 0.5 in. = 367 cubic feet (about 13.6 cubic yards)
Skip the manual math — enter your numbers into the calculator above and it handles the conversion automatically.
How much compost should I add? (by project type)
| Project | Recommended depth | Notes |
|---|---|---|
| New garden bed | 1–2 in (heavy: up to 3 in) | Till into top 6–8 in of existing soil |
| Raised bed | 1–2 in | Cap at ~25–30% compost in the total mix |
| Established lawn (topdressing) | ¼–½ in | Apply after aerating for best results |
| New lawn | 1–2 in | Mix into topsoil before seeding or sodding |
| Potted plants / containers | 25–30% of pot volume | Blend with potting soil, don't use pure compost |
| Mulch layer around plants | 2–3 in | Keep clear of stems and trunks |
How is compost measured and sold?
Compost is sold two ways: bagged (typically 1 cubic foot per bag, sometimes 1.5 or 2 cubic feet) or bulk (by the cubic yard, delivered by truck). For small beds and containers, bags are usually more convenient and let you buy the exact amount. Once you're past roughly 2 cubic yards, bulk delivery is almost always cheaper — the calculator's cubic yard figure is what you'd quote to a supplier.
One cubic foot of compost weighs roughly 40 lbs (about 18 kg), though this varies with moisture content and material — the weight result above uses a standard bulk density so you know what a delivery will actually weigh, which matters if a truck needs to access a soft driveway or a rooftop garden has a load limit.
How much does compost cost?
Bagged compost typically runs $4–6 per cubic-foot bag. Bulk compost is cheaper per unit — often $25–45 per cubic yard before delivery — but usually has a minimum order. Enter your own local price per unit into the calculator to get an exact total instead of a national average.
Can I make my own compost instead of buying it?
Yes — home composting is free and reduces food waste. You'll need a mix of "browns" (dry leaves, cardboard, straw) and "greens" (food scraps, grass clippings) at roughly a 30:1 carbon-to-nitrogen ratio. A basic backyard pile typically takes a few months to a year to finish; a tumbler composter can produce usable compost in as little as 8–12 weeks with regular turning. What you can't compost: meat, dairy, and oily foods, which attract pests and slow decomposition.
FAQ
How much compost do I need per square foot?
For most garden beds, plan on 1–2 inches of compost per square foot of area, which works out to roughly 0.15–0.3 cubic feet of compost per square foot. Use the calculator above with your exact area to get a precise figure.
How many bags of compost do I need for a raised bed?
A raised bed filled with 1–2 inches of compost typically needs 1 standard 1-cubic-foot bag per 6–12 square feet, depending on depth. A typical 4×8 ft raised bed at 1.5 inches needs about 4 bags.
Is more compost always better?
No. Cap compost at roughly 25–30% of the total soil mix. Pure or excessive compost can hold too much water, throw off nutrient balance, and actually harm plant roots.
What's the difference between compost and topsoil?
Topsoil is mineral-based soil used as a growing medium; compost is decomposed organic matter used as a soil amendment. Compost is mixed into topsoil, not used in place of it.
How long does bagged compost last before use?
Bagged compost can be stored for several months to a year in a dry, shaded spot without losing much quality, though it's best used within the same growing season.