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Landscaping & YardCompost Calculator — How Much Compost Do I Need?
Enter the area and how thick you want to spread compost to get cubic yards and the number of standard bags — for top-dressing beds, amending soil, or feeding a lawn.
How this calculator works
Volume = area × depth. We convert to cubic yards and divide the cubic feet by 1.5 (a common bag size) to count bags. Compost is light, so bulk delivery is economical for larger jobs.
What changes how much you need
- Top-dressing a lawn: ¼–½ inch. Amending beds: 1–3 inches worked into the soil.
- Raised beds: blend roughly 1 part compost to 3 parts topsoil.
- Bag sizes vary (1, 1.5, and 2 cu ft) — check the label and adjust.
- Compost settles and breaks down; reapply seasonally.
- A cubic yard weighs roughly 1,000–1,400 lb — much lighter than soil, but still past a half-ton pickup’s payload.
Compost coverage by depth
Lawn top-dressing is the thin end on purpose: more than about ½ inch at once smothers the grass crowns. Bed amendment goes on thicker because it gets worked into the top 6 inches of soil rather than left on the surface.
| Depth | Sq ft per cubic yard | Sq ft per 1.5 cu ft bag | What it is for |
|---|---|---|---|
| ¼ in | 1,296 sq ft | 72 sq ft | Top-dressing an established lawn |
| ½ in | 648 sq ft | 36 sq ft | Heavier lawn top-dress, over-seeding prep |
| 1 in | 324 sq ft | 18 sq ft | Mulching beds, light soil amendment |
| 2 in | 162 sq ft | 9 sq ft | Amending a bed, worked into the top 6 inches |
| 3 in | 108 sq ft | 6 sq ft | Building a new bed out of poor soil |
Bags per cubic yard by bag size
Bag counts round up to whole bags. Above about a cubic yard — 18 standard bags — bulk delivery is usually cheaper per unit and leaves you no plastic to dispose of.
| Bag size | Bags per cubic yard | Bags per 100 sq ft at 1 in | Bags per 100 sq ft at ¼ in |
|---|---|---|---|
| 1 cu ft | 27 | 9 | 3 |
| 1.5 cu ft (most common) | 18 | 6 | 2 |
| 2 cu ft | 14 | 5 | 2 |
| 3 cu ft | 9 | 3 | 1 |
Compost needed by job
The raised-bed row is the compost share of a 1-part-compost-to-3-parts-topsoil blend, not the whole bed volume.
| Job | Area | Depth or blend | Cubic yards | 1.5 cu ft bags |
|---|---|---|---|---|
| Amend a vegetable bed · 4 × 8 ft | 32 sq ft | 2 in | 0.2 | 4 |
| Fill a new raised bed · 4 × 8 ft, 12 in deep | 32 sq ft | 1:3 with topsoil | 0.3 | 6 |
| Amend a border bed · 20 × 4 ft | 80 sq ft | 2 in | 0.5 | 9 |
| Top-dress a small lawn | 1,000 sq ft | ¼ in | 0.8 | 14 |
| Over-seeding prep | 2,000 sq ft | ½ in | 3.1 | 56 |
| Top-dress a typical lawn | 5,000 sq ft | ¼ in | 3.9 | 70 |
Frequently asked questions
How thick should I spread compost?
¼–½ inch to top-dress a lawn, or 1–3 inches dug into garden beds.
How many bags of compost in a yard?
About 18 bags at 1.5 cubic feet each (27 ÷ 1.5), or ~14 bags at 2 cubic feet.
Can I fill a raised bed with only compost?
It’s best mixed — pure compost holds too much water and settles. Blend about 1 part compost to 3 parts topsoil.
How much compost do I need to top-dress 1,000 sq ft of lawn?
At the standard ¼ inch, about 21 cubic feet — roughly 0.8 cubic yards, or 14 bags of 1.5 cu ft. Rake or drag it in so the grass blades still show through; burying the crowns is what kills patches.
How much does a cubic yard of compost weigh?
Roughly 1,000–1,400 lb — half to three-quarters of a ton — depending on moisture and how much sand or soil is blended in. That is already past what a half-ton pickup should carry, so a 3-yard order needs a dump delivery.
What is the right compost-to-soil ratio for a raised bed?
About 1 part compost to 3 parts topsoil for a general-purpose mix. A 4 × 8 ft bed 12 inches deep is 32 cubic feet, so roughly 8 cubic feet of compost (6 bags) and 24 cubic feet of topsoil. Pure compost shrinks as it finishes breaking down, holds too much water, and can be too high in salts for seedlings.
When is the best time to apply compost?
Early spring or early fall for lawns, when the grass is growing actively and can knit up through the layer. Beds can be top-dressed any time the soil is not frozen or waterlogged; if you are working it in, do it a few weeks before planting.
Is compost the same as topsoil?
No. Compost is decomposed organic matter — an amendment that feeds soil biology and improves structure. Topsoil is mineral soil that gives you bulk and volume. Use topsoil to fill or raise a grade and compost to improve what is already there; blends sold as "garden soil" are a mix of both.