How Much Mulch and Soil to Order

To determine how much mulch and soil to order, multiply the area you need to cover by the depth of material you need to add. With area in square feet and depth in inches, divide their product by 324 to get cubic yards. For mulch, calculate only the additional layer needed; for soil, measure the space between the existing soil surface and your intended fill level. Convert that volume into your supplier’s bulk-order increment or the actual volume printed on each bag.

Mulch and Soil Quantities by Coverage Depth

These are calculated volumes for a uniform layer, using 27 cubic feet per cubic yard. Cubic-yard figures are rounded to two decimal places; bag counts are rounded up from the unrounded volume. The 6- and 12-inch rows illustrate soil-fill quantities, not recommended mulch depths.

Choose the Depth Before Calculating the Order

The same area can require very different quantities depending on the depth. A 100-square-foot bed needs 16.67 cubic feet at 2 inches deep but 25 cubic feet at 3 inches deep—a 50% increase. Choosing an appropriate depth matters more than rounding the final answer to another decimal place.

Mulch: Measure the Total Layer Already in Place

Iowa State University Extension recommends a general organic-mulch depth of 2–4 inches, depending on the material, soil texture, climate, and planting. Its guidance identifies 2–3 inches as suitable for shredded bark, with coarser materials generally toward the deeper end and finer materials toward the shallower end. These are starting points for choosing a depth, not a reason to apply every mulch product at 4 inches.

Before ordering replacement mulch, check the existing layer in several places. If your chosen total depth is 3 inches and approximately 2 inches of usable mulch remain, calculate a 1-inch addition—not a new 3-inch layer.

Where the old layer varies substantially, divide the bed into sections and calculate each section separately. This avoids ordering enough to cover the thinnest spot at full depth across the entire property.

A larger mulch order is not automatically better for plants. Iowa State University Extension warns that excessively deep mulch can contribute to waterlogging and reduced soil oxygen. Keep mulch away from tree trunks rather than using surplus material to build a mound around them.

Soil: Measure the Actual Space You Need to Fill

For a raised bed, use the inside length and width, not the outside dimensions of the frame. Measure vertically from the existing soil surface to the intended finished soil level. If you want space below the rim for a separate mulch layer, leave that space out of the soil calculation.

An empty bed and a partially filled bed require different orders even when their frames are identical. A bed with 12-inch sides does not necessarily need 12 inches of purchased soil.

The growing medium also depends on what is beneath the bed. University of Maryland Extension distinguishes beds over native soil from beds on hard surfaces. For its compacted-soil scenario, it recommends compost and purchased topsoil in a 1:2 or 1:1 ratio; for beds on a non-permeable surface, it recommends a different approach using compost and soilless growing mix. Do not treat one soil recipe as suitable for every raised bed.

Measure the Area and Calculate the Volume

Use the following process for each material. Keep mulch, topsoil, compost, and any purchased soil blend on separate order lines unless you are buying a premixed product.

1. Measure the area to receive material. For a rectangular bed, multiply length by width in feet. Exclude patios, stepping stones, and other areas you will not cover.
2. Break irregular beds into simpler shapes. Calculate rectangles, triangles, or circles separately, then add their areas without counting overlapping sections twice.
3. Determine the depth to add in inches. For mulch, subtract the usable existing layer from your chosen total depth. For soil, measure the remaining fill space.
4. Calculate cubic feet or cubic yards. Use consistent units and retain the unrounded result until the purchasing step.
5. Convert the result into bags or bulk quantities. Use the actual package volume or the supplier’s available order increments.

Area Formulas for Common Bed Shapes

For a circular bed, the radius is half the diameter. For a ring-shaped bed, subtract the inner area that will remain uncovered.

Volume Formulas

Let (A) be the area in square feet and (D) be the added depth in inches:

[
\text{Cubic feet}=\frac{A\times D}{12}
]

[
\text{Cubic yards}=\frac{A\times D}{324}
]

The first formula converts inches to feet. The second also converts cubic feet to cubic yards: (12\times27=324). Mississippi State University Extension describes this area-times-depth method and confirms that 1 cubic yard equals 27 cubic feet.

For a rectangular bed, you can combine the measurements directly:

[
\text{Cubic yards}=\frac{L\times W\times D}{324}
]

These formulas assume a uniform depth. If the ground slopes or the fill space is uneven, calculate separate sections using their measured depths rather than applying one maximum depth everywhere.

Convert the Volume Into Bags or a Bulk Order

Bulk mulch is commonly sold by the cubic yard, while bagged mulch is sold by cubic feet. Mississippi State University Extension gives examples of different bag sizes, so a bag count is meaningful only when the package volume is specified.

Calculate Bags From the Package Volume

[
\text{Bags needed}=
\left\lceil
\frac{\text{Required cubic feet}}{\text{Cubic feet per bag}}
\right\rceil
]

The ceiling symbol means to round up to the next whole bag.

For example, a calculated requirement of 25 cubic feet would take:

These package sizes illustrate the calculation; they do not describe a specific product. Check the volume on the bag you intend to buy.

A package’s stated coverage is useful only at its stated application depth. A 2-cubic-foot bag mathematically covers 12 square feet at 2 inches deep but only 8 square feet at 3 inches deep. Using the 2-inch coverage figure for a 3-inch installation would leave you short.

Keep Weight and Volume Separate

Your calculation produces a volume, not a weight. If a soil product is labeled only in pounds, obtain its volume or appropriate density information from the manufacturer or supplier before converting your requirement into packages.

Likewise, if a bulk supplier quotes soil by the ton, ask for a conversion appropriate to that specific material. A cubic yard and a ton are not interchangeable units, and the volume-to-weight relationship depends on the material and its condition.

Compare the Complete Purchasing Options

Request quotes for the same calculated volume and material specification. For bulk delivery, confirm the minimum order, available increments, delivery charge, and unloading location. For bags, compare the total package volume—not just the price per bag.

Bags can make a small order or a difficult-access project easier to handle. Bulk delivery may reduce packaging and individual bag handling, but the delivery location and movement of material across the property still affect the practical choice.

Worked Example: Mulch for Several Landscape Beds

This hypothetical project has three beds totaling 480 square feet. The chosen application depth is 3 inches, and no usable mulch remains.

First, calculate cubic feet:

[
480\times\frac{3}{12}=120\text{ cubic feet}
]

Then convert to cubic yards:

[
120\div27=4.444\ldots\text{ cubic yards}
]

The calculated requirement is approximately 4.44 cubic yards, or:

[
120\div2=60\text{ bags of 2 cubic feet each}
]

If the supplier sells bulk mulch in half-cubic-yard increments, an order of 4.5 cubic yards would meet this calculated requirement. That increment is an example purchasing condition, not a standard followed by every supplier.

The Same Beds With Existing Mulch

Suppose the same 480-square-foot area already has a reasonably uniform 2-inch layer of usable mulch. To reach the chosen 3-inch total depth, calculate only the 1-inch addition:

[
480\times\frac{1}{12}=40\text{ cubic feet}
]

[
40\div27=1.481\ldots\text{ cubic yards}
]

That is approximately 1.48 cubic yards or 20 bags of 2 cubic feet each. With hypothetical half-yard bulk increments, the corresponding order would be 1.5 cubic yards.

Checking the existing layer changes the calculated order from 4.44 to 1.48 cubic yards. This is why a refresh should not automatically use the same quantity as the original installation.

Worked Example: Soil for a Raised Bed

This hypothetical raised bed measures 4 feet by 8 feet internally and needs 10 inches of additional growing medium to reach the intended fill line. The example illustrates purchasing volume; it does not establish a universal planting-depth recommendation.

Calculate the volume:

[
4\times8\times\frac{10}{12}
=26.666\ldots\text{ cubic feet}
]

Convert to cubic yards:

[
26.666\ldots\div27
=0.98765\ldots\text{ cubic yards}
]

The calculated requirement is approximately 26.67 cubic feet, or 0.99 cubic yard.

Possible purchasing quantities are:

• 1 cubic yard of a suitable premixed growing medium, providing 27 cubic feet.
• 18 hypothetical 1.5-cubic-foot bags, also providing 27 cubic feet.
• 14 hypothetical 2-cubic-foot bags, providing 28 cubic feet.

Those quantities meet the geometric fill requirement. They do not include a separately determined allowance for settling.

Splitting the Order Into Soil and Compost

If the site conditions match University of Maryland Extension’s compacted-soil scenario and you choose its 1:2 compost-to-topsoil option, divide the total volume into three equal parts. One part is compost and two parts are topsoil. The institution also provides a 1:1 option and different guidance for other bed conditions.

For this example:

[
\text{Compost}=26.666\ldots\times\frac{1}{3}
=8.888\ldots\text{ cubic feet}
]

[
\text{Topsoil}=26.666\ldots\times\frac{2}{3}
=17.777\ldots\text{ cubic feet}
]

If both materials were available in hypothetical 1.5-cubic-foot bags, six bags of compost and 12 bags of topsoil would provide 27 cubic feet while preserving the selected 1:2 ratio.

If you buy a premixed product instead, order the total required blend volume. Do not also order the component quantities as though they were additional material.

Allow for Site Uncertainty Without Overfilling

The calculated volume describes the space to cover or fill. The actual purchase may need adjustment for uneven ground, measurement uncertainty, material settling, or supplier order increments.

Do not automatically add the same percentage to every mulch and soil order. Instead:

• Recheck uncertain measurements before buying extra material.
• Ask the supplier whether its volume is measured loose and whether it provides product-specific settling guidance.
• Decide where any surplus will go before increasing the order.
• Separate purchasing surplus from application depth; extra mulch should not be spread simply to use it up.

For purchased topsoil, University of Maryland Extension recommends asking a reputable supplier about the soil’s origin, soil-test results, mixing, and storage, and examining the material before purchase or delivery. The correct quantity will not compensate for unsuitable growing medium.

Check These Details Before Placing the Order

• I measured only the areas that will actually receive material.
• I used inside dimensions for raised beds.
• I calculated added depth rather than automatically using the full frame height or a new full mulch layer.
• I kept length and width in feet and depth in inches for the formulas shown here.
• I calculated sections separately where depths differ.
• I checked the actual volume of each bag.
• I kept mulch, soil, compost, and premixed growing medium as separate purchasing items.
• I confirmed bulk minimums, order increments, delivery access, and the unloading location.
• I have a plan for any surplus rather than overfilling beds or applying mulch too deeply.

Order from the measured volume, then round to a purchasable quantity. Keep the intended application depth unchanged unless the site or material guidance gives you a reason to revise it.