Guide · Garden
How Much Topsoil for a Raised Garden Bed?
A 4×8-foot raised bed filled 12 inches deep needs about 1.2 cubic yards of soil — roughly 22 bags at 1.5 cubic feet each. A shallower 4×8 bed at 10 inches deep needs about 1 cubic yard, or 18 bags — order 20 to cover settling.
Below is the volume formula, a chart covering common bed sizes and depths, bag-vs-bulk guidance, and the settling allowance most people forget. To skip the arithmetic, use our free topsoil and compost calculator — enter your bed dimensions and it returns cubic yards and bag counts instantly.
Cubic yards and bag counts for your exact bed size — free, no sign-up.
Open the topsoil calculator →For a 4×8 bed 12″ deep (1.5-cu-ft bags). Add ~10% for settling: order 1.3 yd or 24 bags.
The math, step by step
= 4 × 8 × (10 ÷ 12) = 26.67 cu ft
Cubic yards = 26.67 ÷ 27 = 0.99 → ~1 cu yd
Bags (1.5 cu ft) = 26.67 ÷ 1.5 = 17.78 → 18 bags
With 10% settling allowance: 18 × 1.10 = 19.8 → 20 bags
- Measure in feet. Length × width × depth, with depth converted from inches: 10″ = 10 ÷ 12 = 0.833 ft.
- Multiply for cubic feet. 4 × 8 × 0.833 = 26.67 cubic feet of soil.
- Convert to cubic yards. One cubic yard = 27 cubic feet: 26.67 ÷ 27 = 0.99 → about 1 yard. Bulk soil is sold by the yard, so this is your bulk order quantity.
- Convert to bags. Divide cubic feet by the bag size: 26.67 ÷ 1.5 = 17.78 — you can’t buy eight-tenths of a bag, so round up to 18 bags.
- Add the settling allowance. Fresh soil consolidates 10–20% in the first season: 18 × 1.10 = 19.8 → buy 20 bags (or order 1.1 yards bulk).
Soil chart for common raised bed sizes
Bag counts assume 1.5-cubic-foot bags and are rounded up — before the settling allowance, so add ~10% when ordering.
| Bed size | Depth | Cubic feet | Cubic yards | 1.5-cu-ft bags |
|---|---|---|---|---|
| 4 × 4 ft | 6″ | 8 | 0.30 | 6 |
| 4 × 4 ft | 12″ | 16 | 0.59 | 11 |
| 3 × 6 ft | 8″ | 12 | 0.44 | 8 |
| 4 × 8 ft | 6″ | 16 | 0.59 | 11 |
| 4 × 8 ft | 10″ | 26.7 | 0.99 | 18 |
| 4 × 8 ft | 12″ | 32 | 1.19 | 22 |
| 4 × 12 ft | 12″ | 48 | 1.78 | 32 |
One cubic yard = 27 cubic feet = 18 bags at 1.5 cu ft. Bulk yards are usually sold in whole or half yards.
Bags or bulk delivery?
The crossover sits around one cubic yard. Below that — a single 4×4 bed, a couple of small planters — bags win on convenience: no delivery fee, no minimum, no pile of dirt on the driveway. Past a yard, bulk is meaningfully cheaper per cubic foot and spares you from hauling and ripping open dozens of bags (a 4×12 bed at 12 inches is 32 bags). Bulk yards also let you order the good stuff: many landscape suppliers sell a pre-blended raised-bed mix, while bagged “topsoil” quality varies wildly by brand. One caution with bulk: confirm whether the price includes delivery, and have a tarp ready — a yard of soil is a bigger pile than most people picture.
Timing matters too. Order soil a week or two before planting so it has time to settle with a good watering — fill the bed, soak it thoroughly, let it sit a few days, then top off the low spots before transplanting. And if you’re gardening in the same spot year after year, a basic soil test every couple of seasons (your local extension office usually offers them cheap) tells you whether you need compost, lime, or sulfur instead of guessing.
Don’t forget settling
Freshly filled beds sink. Between consolidation, watering, and organic matter breaking down, expect the soil level to drop 10–20% in the first season — a bed filled flush to the top in spring sits a couple of inches low by fall. Order about 10% more than the raw volume math says, fill the bed slightly crowned (mounded an inch or two above the frame), and plan to top it off with compost after the first growing season. This is the single most common reason gardeners make a second soil run, and it’s entirely avoidable.
What should you actually fill it with?
Straight bagged topsoil is the default purchase and the mediocre choice: it compacts, drains inconsistently, and brings weed seeds along for the ride. Better options:
- Raised-bed mix (best default) — topsoil blended with compost and sometimes aeration amendments. Many bulk suppliers sell exactly this.
- DIY blend — roughly 2–3 parts topsoil to 1 part compost, mixed in the bed or on a tarp before filling.
- Hugelkultur base for deep beds — for beds 12 inches or deeper, fill the bottom third with logs, branches, and leaves. It displaces expensive soil now, then decomposes into rich organic matter over a few seasons. Skip treated lumber and black walnut.
Whatever you use, keep the topsoil and compost calculator handy when blending — it handles the compost fraction too. And if you’re adding drip lines before planting, our drip irrigation calculator sizes the watering layout for the bed.
How we calculate
Soil volume is length × width × depth in consistent units (depth converted from inches to feet), divided by 27 for cubic yards. Bag counts divide cubic feet by the bag size (1.5 cu ft) and round up; one cubic yard equals 18 such bags. The 10% settling allowance is a planning rule of thumb — actual settling depends on soil composition, moisture, and how much organic matter breaks down in the first season. These are planning figures, not engineering specifications.
Reviewed September 2026 · TrueMeasure
Frequently asked questions
How many bags of topsoil are in a cubic yard?
18 bags at 1.5 cubic feet each (27 ÷ 1.5 = 18). For 1-cubic-foot bags it is 27 bags; for 2-cubic-foot bags, about 13.5.
Should I buy topsoil in bags or in bulk?
Bulk wins past about 1 cubic yard — it is cheaper per yard and avoids a mountain of plastic bags. Under that, bags are more convenient and easier to transport.
Will the soil in my raised bed settle?
Yes — expect 10 to 20 percent settling in the first season as the soil consolidates and organic matter breaks down. Order about 10 percent extra and top the bed off after a few months.
Can I use plain topsoil for a vegetable garden?
A raised-bed or garden mix (topsoil blended with compost) performs better — straight topsoil can compact and drain poorly. Blend in compost at roughly one part compost to two or three parts topsoil.
How deep should a raised garden bed be?
6 inches works for herbs and lettuce; 10 to 12 inches suits tomatoes, peppers, and root vegetables. Deeper beds hold more moisture and need less frequent watering.
What can I put in the bottom of a deep bed to save soil?
Logs, branches, and leaves — the hugelkultur method — for beds 12 inches or deeper. They take up volume, then slowly break down and feed the soil. Avoid treated lumber and black walnut.