A 4x8 raised bed needs 32 cubic feet of soil, or about 1.2 cubic yards
The amount of soil you need depends on how deep you fill the bed. A standard depth is 12 inches (one foot). At that depth, a 4-foot-by-8-foot bed holds exactly 32 cubic feet of soil. If you go deeper — say 18 inches for root vegetables — you'll need 48 cubic feet. If you're doing a shallow bed for greens at 8 inches, you'll need about 21 cubic feet.
Most garden centers and soil suppliers sell by the cubic yard, not cubic feet. One cubic yard equals 27 cubic feet. So 32 cubic feet is roughly 1.2 cubic yards. When you order, round up to 1.5 cubic yards to account for settling and to may support you have enough to fill corners and edges completely.
The math is straightforward: length × width × depth (all in feet) = cubic feet needed. For a 4×8 bed at 12 inches deep, that's 4 × 8 × 1 = 32 cubic feet.
Key Takeaways
- A 4x8 raised bed filled 12 inches deep requires 32 cubic feet of soil, which equals about 1.2 cubic yards.
- Order 1.5 cubic yards when buying from a supplier to account for settling and may support complete coverage.
- Deeper beds for root crops need more soil: 18 inches deep requires 48 cubic feet, or about 1.8 cubic yards.
- Shallower beds for lettuce and greens need less: 8 inches deep requires 21 cubic feet, or about 0.8 cubic yards.
- Soil settles after watering, so filling to the brim initially means you'll have room to add mulch or compost later.
Why depth matters more than you might think
The depth you choose affects not just how much soil to buy, but what you can grow. Shallow-rooted crops like lettuce, spinach, and herbs do fine in 8 to 10 inches. Most vegetables — tomatoes, peppers, beans, squash — need 12 inches minimum. Root vegetables like carrots, beets, and parsnips want 16 to 18 inches so the roots have room to develop without hitting the bottom of the bed.
If you're building a bed for mixed vegetables, 12 inches is the practical middle ground. It's deep enough for most crops, doesn't require an enormous amount of soil, and is straightforward to manage when weeding or harvesting. If you plan to grow only greens and herbs, you can save money by going shallower.
Keep in mind that soil settles over time, especially after the first watering. A bed filled to the brim at 12 inches will drop to about 11 inches after a week or two. This is normal and not a problem — it just means you have room to add a layer of mulch or compost later in the season.
Calculating soil for different bed depths
| Bed Depth | Cubic Feet Needed | Cubic Yards Needed | Order This Much | Best For |
|---|---|---|---|---|
| 8 inches | 21 cubic feet | 0.8 cubic yards | 1 cubic yard | Lettuce, spinach, herbs |
| 10 inches | 27 cubic feet | 1 cubic yard | 1.25 cubic yards | Shallow greens and herbs |
| 12 inches | 32 cubic feet | 1.2 cubic yards | 1.5 cubic yards | Most vegetables |
| 18 inches | 48 cubic feet | 1.8 cubic yards | 2 cubic yards | Carrots, beets, parsnips |
What type of soil to buy
You have three main options: topsoil, garden soil, and raised bed mix. Topsoil is the upper layer of natural soil, usually sold by itself. It's cheaper but often compacts over time and may contain weed seeds. Garden soil is topsoil blended with compost and other organic matter — it drains better and holds nutrients longer than plain topsoil. Raised bed mix is a blend designed specifically for containers and raised beds, usually containing topsoil, compost, peat moss or coco coir, and perlite for drainage.
For a 4x8 bed, raised bed mix costs more per cubic yard but performs better long-term because it won't compact as much and drains more evenly. If budget is tight, a 50-50 blend of topsoil and compost works well and costs less than a pre-made raised bed mix. Avoid pure compost — it's too rich and drains poorly on its own.
Many suppliers deliver soil in bulk, which saves money if you're ordering 1.5 cubic yards or more. Check whether delivery is free or has a minimum order. Some garden centers also sell bagged soil if you prefer to haul it yourself — you'd need about 48 bags of 2-cubic-foot soil to fill a 12-inch-deep 4x8 bed, which is heavy and time-consuming but sometimes cheaper for small orders.
Filling your bed efficiently
When the soil arrives, spread it evenly across the bed rather than dumping it in one corner. Use a shovel or garden fork to break up any compacted areas as you go. Fill to the top edge, then water thoroughly — the soil will settle, and you can add more if needed. Don't be alarmed if it drops an inch or two; that's settling, not a mistake.
If you're mixing your own blend (topsoil and compost, for example), do it in the bed itself. Spread the topsoil first, then the compost, then mix them together with a garden fork. This is easier than mixing in a pile and then moving it. If you're using a pre-made raised bed mix, just spread and level it.
After filling, let the bed sit for a few days before planting if possible. This gives the soil time to settle and allows you to see if you need to add more. If you're planting right away, water gently after planting to help the soil settle around the roots.
Accounting for settling and future amendments
Soil settles most dramatically in the first month. After that, it settles more slowly. Plan to add a 1 to 2-inch layer of compost each spring to replenish nutrients and maintain depth. Over a season or two, you may need to top up the bed once or twice, especially if you're growing heavy feeders like tomatoes or squash.
This is why ordering slightly more than the bare minimum (1.5 cubic yards instead of exactly 1.2) is practical. You'll use the extra for settling, and you'll have some left over for amendments. If you have leftover soil, store it in bags or a bin for next season — it won't spoil.
Common mistakes when ordering soil
The biggest mistake is ordering too little. Many people calculate exactly 32 cubic feet for a 12-inch bed and then run short because they didn't account for settling or the fact that soil doesn't pack perfectly into corners. Order 1.5 cubic yards and you'll have enough.
Another common error is confusing cubic feet with square feet. A 4x8 bed has 32 square feet of surface area, but you need 32 cubic feet of soil at 12 inches deep — these are different measurements. Square feet tells you the footprint; cubic feet tells you the volume.
A third mistake is buying pure topsoil and expecting it to perform like a raised bed mix. Topsoil alone compacts easily and doesn't drain as well. If you're on a budget, blend it with compost rather than using it straight.
Frequently Asked Questions
Can I use less soil if I put cardboard or newspaper at the bottom?
Cardboard at the bottom doesn't reduce the amount of soil you need — you still need the full depth for roots. Cardboard is useful for blocking weeds from below, but it doesn't replace soil volume. You'll still need 32 cubic feet for a 12-inch-deep 4x8 bed.
What if I want to fill my bed partially and add more soil later?
You can do this, but it's less efficient. Soil settles unevenly if you add it in stages, and you may end up with compacted layers. If you must fill in stages, water between layers and wait a few days for settling before adding the next layer.
How much does 1.5 cubic yards of soil weigh?
Dry soil weighs about 1,300 to 1,500 pounds per cubic yard, so 1.5 cubic yards is roughly 2,000 to 2,250 pounds. Wet soil is heavier. This matters if you're hauling it yourself — most pickup trucks can handle it, but check your vehicle's capacity before ordering.
Do I need to mix the soil with anything before planting?
If you're using a pre-made raised bed mix, no — it's ready to plant. If you're using topsoil alone, mixing in compost (about 25 to 30 percent by volume) improves drainage and adds nutrients. Garden soil blends usually don't need amendment, but adding a thin layer of compost on top before planting never hurts.
Can I reuse soil from last year?
Yes. Refresh it by mixing in 2 to 3 inches of fresh compost before planting. Old soil compacts over time, so the compost loosens it and adds back nutrients that plants used. You don't need to replace all the soil — refreshing the top layer is usually enough.