Compost Calculator

Background: You are creating a new 10 ft × 5 ft raised vegetable bed. The native soil is compacted clay, so you want a heavy dose of compost — about 2 inches deep.

Result: You need about 8.3 cubic feet of compost — that is roughly nine 1-cubic-foot bags. At roughly $5 per bag, expect to spend about $40–$45. The total weight will be around 330 lb (150 kg), so bring a sturdy vehicle.

Background: Your lawn (110 ft × 80 ft) is looking tired. You plan to aerate and then top-dress with a thin ½-inch layer of compost.

Result: This is a bulk-order situation — about 13.6 cubic yards. Buying in bulk will be far more economical than individual bags. At a typical bulk price of $30–$50 per cubic yard, expect to pay $400–$680. Use the Price section to compare with bagged options.

Background: You have a 4 ft × 8 ft raised bed that is 1 ft deep. You want to fill it with a 75% soil / 25% compost mix.

Result: You need 8 cubic feet of compost — that is eight 1-cubic-foot bags. Price: about $40. Enter 4′ × 8′ for the bed dimensions and use “Raised bed — high compost level” to get a recommended depth that matches your plan. Then check the Total cost section.

Background: You need 2 cubic yards of compost for a landscaping project. At the local garden center, bagged compost is $5 per cubic foot. Bulk delivery is $45 per cubic yard.

Bulk cost: $2 \times \$45 = \$90$.

Result: Bulk is one-third the price. Enter the volume, price per cubic foot for bagged (or per cubic yard for bulk), and toggle between currency units to compare side by side.

Precision settings explained

General best practices

• Always buy a little extra. Compost settles during transport and application. Add 5–10% to the calculator’s volume as a buffer.
• Know your density. The default density (650 kg/m³) is a good average for mature compost, but moisture content and particle size vary a lot. Wet, chunky compost can weigh 800+ kg/m³.
• Use the right depth for the job. Mixing into soil? Go deeper (1–2 in). Surface dressing an existing lawn? Keep it thin (¼–½ in) to avoid smothering the grass.
• Bulk is almost always cheaper. If the calculator shows more than 1–2 cubic yards, call a local landscape supplier for a bulk quote before buying bags at the hardware store.
• Check your soil type. Sandy soil benefits from more compost (retains moisture), while clay soil needs less (improves drainage). Adjust the depth accordingly.

1) Area

Where $A$ is the total area, $L$ is length, and $W$ is width.

2) Volume

Where $V$ is the compost volume, $A$ is area, and $D$ is the depth of the compost layer.

3) Total cost

Where $\text{Tc}$ is the total cost, $P$ is the price per unit volume, and $V$ is the volume. Currency conversion is handled automatically when price and total cost use different currencies.

4) Total weight

Where $\text{Tw}$ is the total weight, $\rho$ is the density (mass per unit volume), and $V$ is the volume.

How do I convert between cubic feet and cubic yards?

There are 27 cubic feet in 1 cubic yard ($1\ \text{yd}^3 = 27\ \text{ft}^3$). To convert, divide the volume in cubic feet by 27. Our calculator handles this automatically — just switch the volume unit in the dropdown.

How much does a cubic foot of compost weigh?

A typical 1-cubic-foot bag of compost weighs about 40 pounds (~18 kg). This matches the default density of 650 kg/m³. Wet compost can be heavier, while dry, screened compost can be lighter. Use the Compost weight section to adjust the density to your specific product.

Can I use this calculator for mulch?

The volume calculation (length × width × depth) works for any material, but the default density is specific to compost. Mulch is typically lighter and fluffier. For a more accurate mulch estimate, try our dedicated Pine Straw Calculator.

Should I use bagged or bulk compost?

For small projects (less than 1–2 cubic yards), bagged compost from a garden center is convenient. For larger projects, bulk delivery is significantly cheaper — often $30–50 per cubic yard compared to $5 per cubic foot for bagged (which works out to $135 per cubic yard!). Use the Price section to compare.

How deep should I apply compost?

It depends on the application:

• New garden beds: 1–2 inches, mixed into the top 6–8 inches of soil.
• Existing lawns: ¼–½ inch as a top-dressing after aeration.
• Raised beds: 1–2 inches of compost mixed with existing soil.
• Potting mix: Aim for about 25% compost, 75% base soil or soilless mix.

Why does the Depth field turn gray sometimes?

When you select a garden or lawn type from the dropdown (anything except “Custom depth”), the depth is automatically set to a recommended value and becomes read-only (gray background). This prevents accidental overrides. Choose “Custom depth” if you want to enter your own value.

Can the calculator handle different currencies?

Yes. The Price and Total cost inputs each have their own currency selector. You can set Price in USD and Total cost in EUR, for example, and the calculator will automatically convert using live exchange rates. Exchange rates are cached for up to 24 hours to ensure quick response times.

What if my garden area is irregularly shaped?

For irregular shapes, break the area into rectangles, calculate each separately, and add the volumes together. For circular or curved areas, measure the approximate length and width of the bounding rectangle — it will get you close enough for compost ordering purposes.

Can I share my calculation results?

Yes! Click the Share button at the bottom of the calculator to generate a link. Check “Include results” to create a URL that preserves all your inputs, outputs, and even the precision setting. Send this link to a landscaper, garden center, or save it for your records.