How Much Soil for a 4x8 Raised Bed? (Quick Chart)
*Quick answer: A 4×8 raised bed at 12 inches deep needs 32 cubic feet of soil — that's about 21 bags (1.5 cu ft each) or 1.2 cubic yards if you buy bulk. Add 10–15% for settling. Don't want to do math? Use the soil volume calculator.
I once bought 15 bags of soil for a 4×8 bed, got home, and ran out with a third of the bed still empty. Drove back, bought 10 more, and had 4 left over. That's $20 sitting in my garage for six months until they got rained on and turned into bricks.
The math is dead simple. I just didn't bother to learn it until my third bed.
Soil Volume for a 4×8 Raised Bed (By Depth)
The formula: Length × Width × (Depth ÷ 12) = cubic feet.
For a 4×8 bed at 12 inches deep: 4 × 8 × (12 ÷ 12) = 32 cubic feet. To convert to cubic yards, divide by 27: 32 ÷ 27 = 1.19 cubic yards.
That's the clean number. In practice, I add 10–15% because soil settles after the first few waterings. For a 32 cu ft bed, that means buying 35–37 cu ft. You'll water your freshly filled bed, come back the next morning, and find 2–3 inches of empty space at the top. Every single time.
Here's every depth you'd realistically build a 4×8 bed at:
| Depth | Cubic Feet | Cubic Yards | Bags (1.5 cu ft) | Bags (2 cu ft) |
|---|---|---|---|---|
| 6" | 16 | 0.59 | 11 | 8 |
| 8" | 21.3 | 0.79 | 15 | 11 |
| 10" | 26.7 | 0.99 | 18 | 14 |
| 12" | 32 | 1.19 | 22 | 16 |
| 18" | 48 | 1.78 | 32 | 24 |
| 24" | 64 | 2.37 | 43 | 32 |
Notice how fast it scales. Going from 12 inches to 18 inches doesn't sound like much, but it's an extra 16 cubic feet — that's 10 more bags or roughly $50–80 more in soil. Think about whether your crops actually need that depth before you build tall.
Soil for Other Common Raised Bed Sizes
Not everyone builds 4×8. Here's a quick reference for the most popular sizes, all in cubic feet:
| Bed Size | 8" Deep | 12" Deep | 18" Deep |
|---|---|---|---|
| 2×4 | 5.3 | 8 | 12 |
| 3×6 | 12 | 18 | 27 |
| 4×4 | 10.7 | 16 | 24 |
| 4×8 | 21.3 | 32 | 48 |
| 4×12 | 32 | 48 | 72 |
Got a weird size? Use the soil volume calculator. It handles any dimensions, including circular beds and L-shapes.
How Many Bags of Soil Do You Need?
Bags come in four common sizes. Here's the bag count for a standard 4×8 bed at 12 inches deep (32 cu ft):
| Bag Size | Bags Needed | Approx Weight per Bag |
|---|---|---|
| 0.75 cu ft | 43 | 15–20 lbs |
| 1.0 cu ft | 32 | 25–35 lbs |
| 1.5 cu ft | 22 | 40–50 lbs |
| 2.0 cu ft | 16 | 50–65 lbs |
One thing that tripped me up: the weight on the label tells you almost nothing about volume. A 40-lb bag of topsoil is about 0.75 cu ft. A 40-lb bag of potting mix might be 1.5 cu ft because it's lighter and fluffier. Check the cubic feet — that's the number that matters.
Those 0.75 cu ft bags? Avoid them. 43 bags for a single bed is a cartoonish amount of plastic waste and at least two SUV loads.
Bags vs Bulk: What's Actually Cheaper?
This is where most people leave money on the table. Here's a real cost comparison for filling a 4×8 bed at 12 inches deep (32 cu ft):
| Option | Unit Cost | Total Cost |
|---|---|---|
| Bagged (1.5 cu ft, premium) | $6–8 per bag | $132–176 |
| Bagged (2 cu ft, store brand) | $4–6 per bag | $64–96 |
| Bulk (per cubic yard) | $30–55 delivered | $36–66 |
The breakpoint is roughly 1 cubic yard (27 cu ft). Below that, bags are more practical — most bulk suppliers have a 1-yard minimum, and delivery fees can eat the savings on small orders. Above 1 yard, call a landscape supply yard. They'll dump a pile in your driveway for a fraction of bag prices.
If you want to save even more, check out the bottom-layer trick in my guide on how to fill a raised bed. Logs, leaves, and straw on the bottom 4–6 inches can cut your soil cost by a third on beds 10 inches or deeper.
How Deep Should Your Raised Bed Be?
This depends on what you're growing, full stop. Here's my cheat sheet after twelve beds:
- 6 inches — lettuce, herbs, radishes, green onions. Fine for shallow-rooted stuff.
- 8 inches — peppers, beans, peas, most greens. Handles 80% of common crops on a tight budget.
- 10–12 inches — tomatoes, squash, cucumbers, broccoli, beets. The sweet spot for a general veggie garden.
- 12–18 inches — carrots, parsnips, potatoes, sweet potatoes. Deep-rooted crops that need room to grow downward.
Don't build 24 inches unless you need accessibility (sitting-height beds) or your native soil is terrible. You're doubling your soil cost for depth most vegetables will never reach.
FAQ
How many 40-lb bags fill a 4×8 raised bed?
A 40-lb bag of topsoil is typically 0.75 cubic feet. For a 4×8 bed at 12 inches deep (32 cu ft), you'd need about 43 bags. That's roughly 1,720 lbs of soil. If you're buying 40-lb bags of potting mix instead, those are usually 1.0–1.5 cu ft per bag — check the volume on the label, not the weight.
Can I fill the bottom with something other than soil?
Yes, and you probably should for beds 10 inches or deeper. I fill the bottom 4–6 inches with logs, dry leaves, and straw, then put the soil mix on top. This is a lazy version of Hügelkultur — the wood holds moisture as it decomposes, and you use 25–30% less purchased soil. I break this down step by step in my raised bed filling guide.
How much does it cost to fill a 4×8 raised bed?
Between $36 and $176 depending on whether you buy bulk or bags. Bulk soil from a landscape supply yard runs $30–55 per cubic yard delivered. You need 1.2 yards for a 4×8 at 12 inches. Bagged soil from a garden center runs $4–8 per bag and you need 16–22 bags. Bulk saves 50–70% on anything over 1 cubic yard.
Do I need to add extra soil for settling?
Yes. Buy 10–15% more than the calculated volume. A 32 cu ft bed will settle to about 28–29 cu ft after the first deep watering. I usually buy 35–37 cu ft worth and top off the next day. If you skip this step, you'll have a bed with 3 inches of empty space above the soil line by the end of the first week.
What's the difference between cubic feet and cubic yards?
One cubic yard = 27 cubic feet. Bags are sold in cubic feet (0.75, 1.0, 1.5, or 2.0 cu ft). Bulk soil is sold in cubic yards. To convert your cubic feet to yards, divide by 27. For a 4×8 at 12 inches: 32 ÷ 27 = 1.19 cubic yards. Most suppliers round up to the nearest quarter-yard, so you'd order 1.25 yards.
Next Steps
- Plug your exact bed dimensions into the soil volume calculator — it handles any size and gives you bag counts automatically.
- Read how to fill a raised bed for the full breakdown on soil mix ratios, bottom-layer tricks, and real cost numbers.
- Need to top off with mulch? The mulch calculator tells you exactly how much to buy.