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 length × width × depth in inches, then divide by 1,728 to get cubic feet. A bed that is 4 feet long, 2 feet wide, and 12 inches deep needs (4 × 2 × 12) ÷ 1,728 = 0.56 cubic feet, or roughly 0.6 cubic feet.
Most garden centers and soil suppliers sell by the cubic yard, not cubic feet. One cubic yard equals 27 cubic feet. If your bed needs 0.6 cubic feet, you would round up and buy one cubic yard, which is more than you need but is the smallest unit most suppliers offer. For multiple beds or larger beds, add up the total cubic feet first, then convert to cubic yards by dividing by 27.
A standard 4-by-8-foot bed with 12-inch depth needs about 32 cubic feet of soil, or just over one cubic yard. A 4-by-4-foot bed at the same depth needs about 16 cubic feet, or roughly 0.6 cubic yards — still a one-yard purchase.
Key Takeaways
- Multiply length × width × depth in inches, then divide by 1,728 to find cubic feet of soil needed.
- Most suppliers sell soil by the cubic yard (27 cubic feet), so you will likely buy more than your exact calculation requires.
- A standard 4-by-8-foot bed at 12 inches deep needs just over one cubic yard of soil.
- Soil settles over time, so filling to the top initially accounts for settling that happens in the first few weeks.
Why depth matters more than you might think
Depth is the biggest variable in your calculation. A 4-by-8-foot bed at 6 inches deep needs only about 16 cubic feet (0.6 cubic yards), but the same bed at 12 inches deep needs 32 cubic feet (1.2 cubic yards). Shallow beds work for herbs and lettuce; deeper beds are necessary for root vegetables like carrots, beets, and potatoes, which need 10 to 14 inches of uncompacted soil.
If your raised bed has a frame that is 12 inches tall, you do not have to fill it completely to the rim. Most gardeners fill to 10 to 11 inches and leave a small lip to prevent soil from washing out during watering. This saves soil and still provides enough depth for most vegetables.
Account for soil settling and compaction
New soil settles noticeably in the first few weeks after you fill a bed, especially if you water it heavily. Plan to fill your bed to the very top initially, knowing that you will lose 1 to 2 inches of depth as the soil compacts. After the first season, you will need to add a fresh layer of compost or topsoil — usually 2 to 3 inches — to restore depth and add nutrients.
Mixing in compost or aged manure when you fill the bed also causes settling. A bed filled with pure topsoil will settle less than one filled with a mix of topsoil and compost, because compost breaks down faster. If you are using a 50-50 mix of topsoil and compost, expect slightly more settling than with topsoil alone.
Buying soil: bulk delivery versus bags
For beds larger than 0.5 cubic yards, bulk delivery from a landscape supplier is usually cheaper per cubic foot than bagged soil. A cubic yard of topsoil delivered costs between $30 and $60 depending on your region and the supplier, while bagged topsoil runs $3 to $8 per bag, and most bags are only 2 cubic feet. A single cubic yard requires 13 to 14 bags, which costs $40 to $112.
Bagged soil is worth buying if you have only one small bed, live in an apartment or townhouse where bulk delivery is not practical, or need to amend soil in an existing bed. For multiple beds or large beds, call three local landscape suppliers, tell them your cubic yardage, and ask for a delivered price. Many suppliers offer free delivery over a certain order size, usually one to two cubic yards.
Check whether the supplier's price includes spreading and grading. Some will dump the soil at the edge of your property; others will spread it into the bed for an extra fee. If you have mobility issues or a very large bed, paying for spreading may be worth it.
Soil quality affects how much you actually need
Not all topsoil is the same. Soil heavy in clay will compact more than soil with more sand or organic matter, meaning you will lose more depth over time and need to amend sooner. Soil that is mostly sand drains too fast and does not hold nutrients well. The best soil for raised beds is a mix: roughly 40 percent topsoil, 40 percent compost, and 20 percent perlite or coarse sand for drainage.
If you are buying pure topsoil, plan to mix in compost at a 1:1 ratio by volume. This means if your bed needs 1 cubic yard of topsoil, buy 0.5 cubic yards of topsoil and 0.5 cubic yards of compost. This costs more upfront but gives you better drainage, more nutrients, and less settling than topsoil alone.
Common bed sizes and soil requirements
| Bed Dimensions | Depth | Cubic Feet | Cubic Yards |
|---|---|---|---|
| 2 × 4 feet | 12 inches | 8 | 0.3 |
| 4 × 4 feet | 12 inches | 16 | 0.6 |
| 4 × 8 feet | 12 inches | 32 | 1.2 |
| 4 × 8 feet | 6 inches | 16 | 0.6 |
| 3 × 6 feet | 12 inches | 18 | 0.7 |
Frequently Asked Questions
Can I use garden soil instead of topsoil?
Garden soil is heavier and more compacted than topsoil, and it often contains clay and existing weeds or pathogens. Topsoil is lighter and better for raised beds. If you use garden soil, mix it with compost to improve drainage and add nutrients. Never use soil from your yard alone, as it will compact hard in a raised bed.
What if I fill my bed and it settles too much?
Add more soil or compost to bring it back to the level you want. You can do this anytime during the growing season, though it is easiest before you plant. After the first year, adding 2 to 3 inches of fresh compost each spring is standard practice and replaces what settled and what plants used.
Do I need to line the bottom of my raised bed?
Lining is optional. A landscape fabric or hardware cloth at the bottom keeps burrowing rodents out but slows drainage slightly. If you have a gopher or mole problem, lining is worth it. Otherwise, soil contact with the ground below is fine and actually helps with drainage and earthworm activity.
How much does a cubic yard of soil weigh?
Topsoil weighs about 1,400 to 1,600 pounds per cubic yard when dry, and more when wet. This matters if you are having soil delivered and need to know whether your driveway or deck can handle it. One cubic yard is roughly the weight of a small car, so do not stack it on a wooden deck or weak driveway.