How much compost to use
Compost is usually spread in thin layers, so the depth you choose matters more than anything else. These are common rates for home gardens; follow your soil test or extension service if they say otherwise.
| Job | Typical layer | Per 100 sq ft |
|---|---|---|
| Lawn top dressing | ¼ in | 2.1 cu ft |
| Yearly top-up of a vegetable or flower bed | 1–2 in | 8.3–16.7 cu ft |
| Mulch layer around shrubs and perennials | 1–2 in | 8.3–16.7 cu ft |
| New bed: worked into the top 6–8 in of soil | 2–3 in | 16.7–25 cu ft |
| Part of a raised bed fill | about 30–50% of the bed volume | see the mix calculator |
The compost formula, worked
cubic feet = area (sq ft) × layer (in) ÷ 12 cubic yards = cubic feet ÷ 27
A 20 × 10 ft vegetable garden with 2 inches of compost (the calculator’s default):
- Area: 20 × 10 = 200 square feet
- Volume: 200 × 2 ÷ 12 = 33.3 cubic feet = 1.23 cubic yards
- With 10% extra: 36.7 cubic feet = 1.36 cubic yards, or 37 bags of 1 cubic foot
Topping up a 4 × 8 ft raised bed with 2 inches: switch to Raised beds and set the soil depth to 2 inches. 4 × 8 × 2 ÷ 12 = 5.3 cubic feet, so six 1-cubic-foot bags. Four beds need 21.3 cubic feet, which is nearly a yard, so bulk may be worth pricing.
Top dressing 1,000 sq ft of lawn at ¼ inch: 1,000 × 0.25 ÷ 12 = 20.8 cubic feet = 0.77 cubic yards. The lawn top dressing calculator covers that job in more detail.
Compost per 1,000 square feet
| Layer | Cubic feet | Cubic yards | 1 cu ft bags |
|---|---|---|---|
| ¼ inch | 20.8 | 0.77 | 21 |
| ½ inch | 41.7 | 1.54 | 42 |
| 1 inch | 83.3 | 3.09 | 84 |
| 2 inches | 166.7 | 6.17 | 167 |
| 3 inches | 250 | 9.26 | 250 |
At an inch or more over a large area, bulk compost by the yard usually beats bags. Below that, bags are easier to handle and store.
Weight of compost
Compost is light compared with soil. A cubic yard weighs very roughly 800 to 1,400 pounds (0.4 to 0.7 tons). Fresh, wet compost sits at the heavy end and dry, screened compost at the light end. The calculator uses the middle of that range for its tons line. If you are hauling it yourself, ask the supplier what their compost weighs, because a wet yard can be much heavier.
Choosing compost
- Finished compost is dark, crumbly and smells earthy. If it smells sour or of ammonia, or you can still see the original scraps, it isn’t ready.
- Screened compost has been sieved to remove sticks and lumps. It spreads more evenly, which matters for lawns.
- What it was made from varies: yard waste, food scraps, manure, or blends. Ask the supplier, and ask if they have a lab analysis, especially for manure-based compost.
- Bagged compost is labelled by volume (cubic feet) or by weight. If the bag only shows a weight, look for a volume elsewhere on the bag before you compare prices.
Compost in raised beds
New raised beds are often filled with a blend that is about a third compost. After that, an inch or two on top each spring replaces what the plants used and what has broken down. Use Raised beds mode with a depth of 1 or 2 inches for that job, or the raised bed soil mix calculator for a new fill.
Compost settles as it is watered and keeps breaking down, so a 2-inch layer will look thinner within weeks. That is normal and part of how it works.
Questions gardeners ask
- How much compost do I need?
- Multiply the area in square feet by the layer depth in inches, divide by 12 for cubic feet, and divide by 27 for cubic yards. A 200 sq ft bed with 2 inches of compost needs 33.3 cubic feet, about 1.23 cubic yards.
- How thick should a layer of compost be?
- Common rates are 2 to 3 inches worked into a new bed, 1 to 2 inches as a yearly top-up on vegetable beds, and about a quarter inch raked into a lawn.
- How much compost do I need for a raised bed?
- For a yearly top-up, 1 to 2 inches: 2.7 to 5.3 cubic feet for a 4 × 8 bed. For a new bed filled with a blend that is 30 percent compost, a 4 × 8 bed 12 inches deep needs about 9.6 cubic feet of compost.
- How much does a cubic yard of compost weigh?
- Roughly 800 to 1,400 pounds, depending mostly on moisture. That is much lighter than topsoil.
- How many bags of compost are in a cubic yard?
- 27 bags of 1 cubic foot, 36 bags of 0.75 cubic feet, 18 bags of 1.5 cubic feet or 13.5 bags of 2 cubic feet.