How far will my compost go?
Enter how many bags or yards you have and how deep you want it.
Plan a compost bin: browns and greens
Enter your bin size to see how much dry material (browns) and wet material (greens) to add, and how much finished compost to expect.
How the compost calculator works
The calculator finds the area of each shape, multiplies by how many you have, subtracts cut-outs, then multiplies by the depth for your project. It adds an allowance for spreading loss and converts to cubic yards, cubic meters and liters. Bag counts, weight, loads and cost all come from that one volume. Below the tool, a bin planner turns a bin size into amounts of browns and greens.
With extra = volume × (1 + extra %)
Cubic yards = cubic feet ÷ 27
Bags = cubic feet ÷ bag size, rounded up
Area formulas used for each shape
| Shape | Formula |
|---|---|
| Rectangle | length × width |
| Circle | π × (diameter ÷ 2)² |
| Triangle | ½ × base × height |
| Known area | entered directly in sq ft (or sq m if you chose meters) |
Worked examples
Example 1: top-dress a 4 × 8 ft raised bed with 2 inches
4 × 8 = 32 sq ft. At 2 in (⅙ ft) that is 5.3 cu ft, or 5.9 cu ft with 10% extra. That is 0.22 cubic yards, or 6 bags of 1 cu ft.
Example 2: top-dress 1,000 sq ft of lawn with ½ inch
1,000 sq ft × (½ ÷ 12 ft) = 41.7 cu ft, or 45.8 cu ft with 10% extra. That is 1.7 cubic yards. Spread it thinly and rake it in so the grass is not buried.
Example 3: a new 20 × 10 ft bed, 3 inches dug in
20 × 10 = 200 sq ft. At 3 in (¼ ft) that is 50 cu ft, or 55 cu ft with 10% extra. That is 2.04 cubic yards, so order 2 yd³ in bulk. The same job in 1 cu ft bags is 55 bags, so bulk is worth pricing.
How deep to spread compost
| Use | Typical depth | Notes |
|---|---|---|
| Lawn top-dressing | ¼ to ½ in | Rake in after aerating; do not smother the grass |
| Established beds and vegetable gardens | 1 to 3 in | Spread on top and mix in gently |
| New beds | 2 to 4 in | Work into the top 6 to 8 in of soil |
| Mulch around trees and shrubs | 2 to 3 in | Keep it back from the trunk |
These are common guides. Rich or fine compost can go thinner, and your soil test may suggest more or less.
How far does a cubic yard of compost go?
| Depth | Area covered by 1 cubic yard |
|---|---|
| ¼ in | 1,296 sq ft |
| ½ in | 648 sq ft |
| 1 in | 324 sq ft |
| 2 in | 162 sq ft |
| 3 in | 108 sq ft |
| 4 in | 81 sq ft |
These are before the extra allowance. Divide 324 by the depth in inches for a quick estimate.
Mistakes to avoid
- Filling a raised bed with 100% compost. Most beds do best with compost mixed into topsoil, often about a third to a half compost. Pure compost can be too rich and can settle a lot.
- Smothering the lawn. Lawn top-dressing is a thin layer, ½ inch at most. Rake it in so the grass blades show through.
- Mixing up depth units. 2 inches is ⅙ foot, not 2. Pick the depth unit in the tool and check the result looks sensible.
- Burying stems and trunks. Pull compost back from plant stems and tree trunks so the bark stays dry.
- Forgetting about settling. Compost settles and some is lost when spreading. A 10% buffer avoids a second trip.
How far does a bag or a yard of compost go?
This table uses bags of 1 cubic foot, which is common for a 40 lb bag of compost. Check the cubic feet printed on your bag. The thin top-dressing depths are for lawns, and 2 to 4 inches suits beds.
| You have | Covers at 0.5 in deep | Covers at 1 in deep | Covers at 2 in deep | Covers at 3 in deep | Covers at 4 in deep |
|---|---|---|---|---|---|
| 10 bags (1 cu ft each) | 240 sq ft | 120 sq ft | 60 sq ft | 40 sq ft | 30 sq ft |
| 20 bags | 480 sq ft | 240 sq ft | 120 sq ft | 80 sq ft | 60 sq ft |
| 27 bags (about 1 cubic yard) | 648 sq ft | 324 sq ft | 162 sq ft | 108 sq ft | 81 sq ft |
| 2 cubic yards | 1,296 sq ft | 648 sq ft | 324 sq ft | 216 sq ft | 162 sq ft |
| 5 cubic yards | 3,240 sq ft | 1,620 sq ft | 810 sq ft | 540 sq ft | 405 sq ft |
No spreading allowance is included here. Add about 10%.
Frequently asked questions
How much compost do I need?
Multiply the area in square feet by the depth in feet, then divide by 27 for cubic yards. A top-dressing of ½ inch on a lawn needs about 1.5 cubic yards per 1,000 square feet, and a 3 inch layer for a new bed needs about 9 cubic yards per 1,000 square feet. The calculator does this for any shape.
How deep should I spread compost?
As a rule of thumb: ¼ to ½ inch over a lawn, 1 to 3 inches on top of established beds and vegetable gardens, and 2 to 4 inches on a new bed, worked into the top 6 to 8 inches of soil. Use the thinner end for rich compost.
How many bags of compost are in a cubic yard?
A cubic yard is 27 cubic feet, so it is 27 bags of 1 cubic foot, 18 bags of 1.5 cubic feet or 14 bags of 2 cubic feet (13.5 rounded up). A 40 pound bag of compost is often about 1 cubic foot, but check the label.
How much does a cubic yard of compost weigh?
Compost is commonly quoted at about 800 to 1,500 pounds per cubic yard, depending on moisture and how fine it is. The calculator uses 40 pounds per cubic foot, about 1,080 pounds per yard, and you can change it.
Is it cheaper to buy compost in bulk or in bags?
Bulk is usually cheaper once you need more than about a cubic yard, but a delivery fee or minimum order can change that. Enter both prices in the calculator to compare for your own project.
What is the difference between compost and mulch?
Compost is fully broken-down organic matter that feeds the soil. Mulch is a coarser surface layer that holds moisture and suppresses weeds, and it breaks down slowly. Compost can also be used as a thin mulch, but it will not last as long.
How much compost do I need for a 4x8 raised bed?
A 4 by 8 foot bed is 32 square feet. Topping it with 2 inches of compost takes about 5.3 cubic feet, or 6 bags of 1 cubic foot. A 1 inch top-dressing is 3 bags, and 3 inches is 8 bags. To fill a new 12 inch bed completely would take 32 cubic feet, but the bed should be filled with a mix of compost and topsoil instead.
How much does a 40 lb bag of compost cover?
A 40 pound bag is often about 1 cubic foot. That covers about 12 square feet at 1 inch deep, 6 square feet at 2 inches, 4 square feet at 3 inches and 3 square feet at 4 inches. Check the cubic feet on your bag because sizes vary.
Can I fill a raised bed with just compost?
It is not usually recommended. Pure compost can hold too many salts and nutrients, compact and shrink as it settles, and dry out unevenly. A common mix is about a third to a half compost with topsoil or similar, and the soil calculator has a mix splitter.
How much compost do I need for 1,000 square feet?
For a lawn top-dressing of ½ inch, about 1.5 cubic yards. For 1 inch, about 3.1 cubic yards. For a 2 inch layer on beds, about 6.2 cubic yards, and for 3 inches about 9.3 cubic yards. Add about 10% for spreading loss.
When is the best time to spread compost?
Spring and fall are the most common times. Spread it on beds before planting or in fall after you clear them, and top-dress a lawn in spring or early fall when the grass is growing.
What goes in a compost bin?
Mix browns, which are dry and carbon-rich, such as leaves, straw and shredded cardboard, with greens, which are wet and nitrogen-rich, such as grass clippings and kitchen scraps. A common guide is about 2 to 3 parts browns to 1 part greens by volume, and a damp, wrung-out-sponge moisture level. Use the bin planner above.
How much finished compost does a compost bin make?
The pile shrinks as it breaks down, so expect roughly a third to a half of the volume you start with. A 3 foot cube bin (27 cubic feet) might make around 9 to 14 cubic feet of finished compost.
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