Calculate soil volume by bed dimensions

The amount of soil you need depends on three measurements: the length, width, and depth of your raised bed. Multiply these three numbers together to get the volume in cubic inches, then convert to cubic feet by dividing by 1,728. Most garden soil is sold by the cubic foot or cubic yard, so this conversion matters for ordering the right amount.

A standard 4-by-8-foot raised bed that is 12 inches deep needs 32 cubic feet of soil. A 4-by-4-foot bed at the same depth needs 16 cubic feet. A 2-by-4-foot bed needs 8 cubic feet. If your bed is deeper — say 18 inches — multiply the cubic footage by 1.5 to account for the extra volume.

Write down your bed's exact dimensions before you shop. Measure the interior space where soil will actually go, not the outer frame. If your bed is not a perfect rectangle, break it into sections, calculate each one separately, and add them together.

Key Takeaways

  • Multiply length × width × depth in inches, then divide by 1,728 to get cubic feet, which is how soil is priced and sold.
  • A 4-by-8-foot bed at 12 inches deep holds 32 cubic feet; a 4-by-4-foot bed at the same depth holds 16 cubic feet.
  • Soil settles over time, so you may need to add more after the first season, especially if you mix in compost or amendments.
  • Buying soil in bulk (by the cubic yard) costs less per cubic foot than buying bags, but requires delivery or a truck.

Bagged soil versus bulk delivery

A standard bag of garden soil holds 2 cubic feet and costs between $3 and $8 depending on brand and location. For a 4-by-8-foot bed at 12 inches deep, you would need 16 bags. Bagged soil is convenient if you have a car and do not mind multiple trips, but the per-cubic-foot cost is higher than bulk.

Bulk soil is sold by the cubic yard — one cubic yard equals 27 cubic feet. A cubic yard typically costs $25 to $50 delivered, depending on your region and whether the supplier charges a delivery fee. For the same 4-by-8-foot bed, you would order just over one cubic yard. Bulk is cheaper per cubic foot but requires either a truck or a delivery charge, which can run $50 to $100 depending on distance.

If you are filling multiple beds or a very large bed, bulk almost always saves money. If you are filling one small bed and have no truck, bags may be the simpler choice despite the higher cost.

Account for settling and amendments

Garden soil settles as it compacts and as organic matter breaks down. In the first season, you may lose 1 to 3 inches of depth, depending on how much compost or aged manure you mixed in. If you plan to amend your soil heavily — adding compost, peat moss, or coconut coir — order 10 to 15 percent extra to account for settling.

Many gardeners do not fill beds with pure garden soil. Instead, they use a mix: perhaps 60 percent garden soil, 30 percent compost, and 10 percent perlite or sand for drainage. If you are mixing, calculate the total volume you need, then divide it among your ingredients. For a 32-cubic-foot bed, that might be 19 cubic feet of soil, 10 cubic feet of compost, and 3 cubic feet of perlite.

After the first season, top-dress your bed with 1 to 2 inches of compost each spring. This replaces what settled and adds nutrients without requiring you to refill the entire bed.

Depth matters for what you grow

Shallow beds work for shallow-rooted crops like lettuce, spinach, and herbs, which need only 6 to 8 inches of soil. Root vegetables like carrots and beets need 10 to 12 inches. Tomatoes, peppers, and squash need 12 to 18 inches because their roots run deep. If you are growing a mix of crops, build to at least 12 inches to give everything enough room.

Deeper beds also hold more moisture and stay warmer in spring and fall, which can extend your growing season. The trade-off is that they require more soil and more weight on the frame, so make sure your bed structure is sturdy enough to hold the load.

Soil weight and frame strength

Wet garden soil weighs about 100 pounds per cubic foot. A 4-by-8-foot bed at 12 inches deep holds 32 cubic feet, which means roughly 3,200 pounds of soil when fully saturated. This is why raised bed frames are built from wood, composite, or metal — they need to withstand significant outward pressure, especially after rain.

If you are using a wooden frame, check that the boards are at least 2 inches thick and that corners are braced or bolted. Thinner boards or weak corners can bow or split under the weight. If you are building a very deep bed or using poor-quality wood, consider adding a center support or using composite materials, which do not rot and handle pressure better over time.

Where to source soil locally

Garden centers and home improvement stores sell bagged soil and often offer bulk delivery. Local landscape supply companies usually have lower bulk prices than big-box retailers. Some municipalities offer free or low-cost compost to residents, which you can mix with purchased soil to reduce cost.

Before ordering, ask whether the soil is screened (free of rocks and debris), whether it contains compost or amendments, and whether it has been tested for contaminants. Soil from unknown sources can carry weed seeds or chemical residue. If you are growing food, ask specifically whether the soil is safe for edibles.

Compare prices from at least two suppliers. The cheapest option is not always the best — very cheap soil may be mostly clay or sand with little organic matter, which will not support plants well. Mid-range soil from a reputable local supplier usually offers better value than the lowest price.

Frequently Asked Questions

Can I reuse soil from last year?

Yes. Remove the top 2 inches and replace it with fresh compost, then reuse the rest. This refreshes nutrients and removes any soil-borne diseases. If your bed had disease problems the previous year, replace more of the old soil or sterilize it by solarizing (covering with plastic in the sun for several weeks).

What if my bed is not a rectangle?

Measure it as if it were divided into rectangles, calculate the volume of each section, and add them together. For a circular bed, measure the diameter, divide by 2 to get the radius, then use the formula: radius squared × 3.14 × depth in feet, divided by 12. Round up slightly to account for settling.

Do I need to line the bottom of my raised bed?

A landscape fabric or hardware cloth lining keeps burrowing pests out and prevents soil from mixing with ground below. It is not required, but it helps if you have gophers, voles, or moles. Fabric alone is enough for most gardens; hardware cloth adds cost but is more durable against determined diggers.

How much does a cubic yard of soil weigh?

Dry soil weighs about 1,300 to 1,500 pounds per cubic yard. Wet soil weighs 2,400 to 2,700 pounds. Ask your supplier for the weight of their specific product, since it varies by composition. This matters if you are calculating truck capacity or whether your deck or patio can support the load.

Can I use potting mix instead of garden soil?

Potting mix is lighter and drains faster, but it is expensive for large beds and breaks down quickly, requiring replacement every year or two. Garden soil is denser and lasts longer. Use potting mix for containers and seed-starting; use garden soil or a garden soil and compost blend for raised beds.