Calculate soil volume by bed dimensions

The amount of soil you need depends on the length, width, and depth of your raised bed. Multiply those three measurements together to get cubic feet, then convert to cubic yards if you're ordering in bulk. A standard 4-by-8-foot bed that is 12 inches deep holds about 32 cubic feet of soil, which equals roughly 1.2 cubic yards.

Most home gardeners fill raised beds to between 10 and 12 inches deep for vegetables, herbs, and flowers. Shallower beds (6 to 8 inches) work for lettuce, spinach, and shallow-rooted greens. Deeper beds (14 to 18 inches) are better for root vegetables like carrots, parsnips, and potatoes, which need room to expand downward without hitting the bottom.

Use this formula: length (feet) × width (feet) × depth (feet) ÷ 27 = cubic yards. If you prefer to work in inches, multiply length × width × depth in inches, then divide by 1,728 to get cubic feet. Soil is usually sold by the cubic yard at garden centers and landscape suppliers, though bags are available for smaller beds.

Key Takeaways

  • A 4-by-8-foot raised bed filled 12 inches deep requires about 1.2 cubic yards of soil, or roughly 32 cubic feet.
  • Vegetables and herbs typically need 10 to 12 inches of soil depth; root crops need 14 to 18 inches.
  • Multiply length × width × depth in feet, then divide by 27 to convert cubic feet to cubic yards for ordering.
  • Bulk soil from landscape suppliers is cheaper per cubic yard than bagged soil, but bagged soil works better for small beds or when you cannot arrange delivery.

Common bed sizes and soil amounts

A 2-by-4-foot bed at 12 inches deep holds 8 cubic feet (0.3 cubic yards). A 3-by-6-foot bed holds 18 cubic feet (0.67 cubic yards). A 4-by-4-foot bed holds 16 cubic feet (0.6 cubic yards). These smaller beds are practical for patios, balconies, or tight garden spaces and can be filled with bagged soil without excessive cost or labor.

Larger beds are more economical per square foot. A 4-by-8-foot bed at 12 inches holds 32 cubic feet (1.2 cubic yards). A 4-by-12-foot bed holds 48 cubic feet (1.8 cubic yards). At this scale, ordering bulk soil from a landscape supplier saves money compared to buying bags, though you will need access for a delivery truck or a way to transport it yourself.

If your bed is not a standard rectangle, break it into sections. An L-shaped or curved bed can be divided into rectangles, calculated separately, then added together. Measure the longest and widest points to get a rough estimate, then refine by sketching the shape on graph paper.

Choosing between bulk soil and bagged soil

Bagged soil costs more per cubic yard but works well for beds under 0.5 cubic yards. A single 2-cubic-foot bag costs between $3 and $8 depending on quality and location. For a 2-by-4-foot bed at 12 inches deep (8 cubic feet), you would need four bags. For a 4-by-8-foot bed (32 cubic feet), you would need sixteen bags, which becomes heavy to move and expensive compared to bulk delivery.

Bulk soil from a landscape supplier typically costs $25 to $50 per cubic yard, delivered. A 1.2-cubic-yard load for a 4-by-8-foot bed costs roughly $30 to $60 delivered, depending on your region and whether the supplier charges a delivery fee. Call ahead to confirm pricing and whether they deliver to residential addresses. Some suppliers have a minimum order (often 0.5 to 1 cubic yard), so very small beds may still be cheaper to fill with bags.

Bagged soil is also easier to handle if you have limited space or cannot accommodate a delivery truck. You can buy bags gradually and store them, then fill the bed over time. Bulk soil arrives all at once and must be spread when ready or it will compact and harden.

Account for settling and compaction

Soil settles over time, especially in the first few weeks after filling. Plan to add 10 to 15 percent extra soil to account for this settling. If your calculation shows you need 32 cubic feet, order 35 to 37 cubic feet to keep the bed at full depth after settling occurs.

Watering accelerates settling. A newly filled bed will drop noticeably after the first heavy watering or rain. Tamp the soil gently with your hands or a board as you fill to reduce settling later, but do not compress it so hard that it becomes dense and airless. The goal is a light, even firmness, not a brick-hard surface.

If you are reusing soil from a previous season, it will have compacted further. Loosen it with a garden fork or tiller before measuring, or plan to add 15 to 20 percent fresh soil to restore volume and structure.

Soil composition and quality matter

The type of soil affects how much you need and how well plants grow. Garden soil is topsoil mixed with compost and organic matter, designed for raised beds. Potting soil is lighter and fluffier, meant for containers, and is more expensive per cubic yard. Topsoil alone is cheaper but often lacks organic matter and may compact heavily.

For most raised beds, a blend works best: 40 percent topsoil, 40 percent compost, and 20 percent peat moss or coconut coir. This mix drains well, holds moisture, and provides nutrients. If you order bulk soil, ask the supplier what is in their "garden soil" mix. Some suppliers sell a ready-made raised-bed blend that is already balanced.

Bagged soil often lists the contents on the label. Look for products that include compost and specify they are for raised beds or vegetable gardens. Avoid bags labeled "potting soil only" unless you are filling a container, as they are too light and expensive for a large bed.

Measure your bed before ordering

Measure the inside dimensions of your raised bed, not the outside. If your bed is made from 2-by-10 boards, the interior width is slightly less than 10 inches because the boards take up space. Use a measuring tape to check the actual inside length, width, and depth. Round to the nearest inch to keep math straightforward.

If you are building the bed and have not yet assembled it, measure the boards themselves and subtract their thickness from your planned dimensions. A bed framed with 2-by-10 boards that you want to be 4 feet by 8 feet will have an interior of roughly 3 feet 9 inches by 7 feet 9 inches if the boards are 0.75 inches thick on each side.

Write down your measurements and keep them. You will need them again when you refresh the soil in future seasons or add amendments.

Frequently Asked Questions

Do I need to fill the entire bed to the top?

No. Most gardeners fill to 10 to 12 inches for general vegetables and herbs. Shallower is fine for greens and lettuce (6 to 8 inches), and deeper is better for root crops (14 to 18 inches). Fill to whatever depth suits what you plan to grow, then add more soil later if you change crops.

Can I mix old soil with new soil to save money?

Yes. Loosen old soil with a fork, mix in fresh compost or garden soil at a 50-50 ratio, and you can reuse it. This refreshes structure and adds nutrients without replacing everything. Do this annually or every other year depending on how depleted the soil looks.

What if I order too much soil?

Extra soil can be spread in garden beds, used to top-dress lawns, or stored in bags or a tarp for next season. Soil keeps well if kept dry. If you order too little, you can add more later, though it may not blend perfectly with the existing soil at first.

Should I put anything under the soil in the raised bed?

A layer of cardboard or landscape fabric at the bottom blocks weeds from below and slows drainage slightly, which can be helpful in very sandy soil. Skip it if your bed sits on solid ground or if you want maximum drainage. It is not required, but many gardeners use it as a weed barrier.

How often do I need to add new soil?

Add 1 to 2 inches of compost or fresh soil each spring to replace what settled and what plants removed as they grew. After three to five years, consider replacing 25 to 50 percent of the soil to restore structure and nutrient content, especially if the bed looks compacted or plants are struggling.