How much soil do I need for a 4×8 raised bed?
A standard 4×8 ft raised bed filled 12 inches deep holds 32 cubic feet of soil — that’s 16 bags at 2 cu. ft. each, or about 1.2 cubic yards in bulk. Before you buy 16 bags, read on: you probably shouldn’t fill it with pure topsoil.
To cover your area 12″ deep you need about 32 cubic feet of topsoil — 16 bags at 2 cu. ft. per bag.
Adjust These Numbers for Your ProjectThe math, step by step
- Your area: 4 × 8 = 32 sq. ft.
- At 12 inches deep: 32 × 1 = 32 cu. ft.
- No waste allowance added.
- Each bag: 2 cu. ft. → 32 ÷ 2 = 16 bags
- Bulk equivalent: 32 ÷ 27 = 1.19 cubic yards
- Loose soil settles — a 5–10% allowance helps if you’re filling or leveling.
- For areas deeper than 6″, bulk delivery by the cubic yard is usually cheaper than bags.
The classic raised-bed fill isn’t 100% topsoil — it’s roughly equal parts topsoil, compost, and a lightener like peat or coco coir (the “Mel’s mix” family), or at minimum two-thirds topsoil and one-third compost. Pure topsoil compacts in a contained bed and drains poorly. So the honest shopping list for this bed is closer to 11 bags of topsoil plus 5 bags of compost than 16 bags of topsoil.
The budget move for deep beds: hügelkultur-lite. Fill the bottom third with untreated logs, branches, and coarse wood chips, then soil mix on top. It cuts the soil purchase by a third, improves moisture retention as the wood breaks down, and settles about an inch a year — which you top up with compost anyway.
Note that soil settles 10–15% in the first season as it compacts and the organic fraction decomposes. Fill the bed to the brim, water it thoroughly, and expect to top it off after a few weeks. That’s normal, not a shortage — but it’s a reason to keep two extra bags on hand rather than cutting the order exactly to the math.
Frequently asked questions
How many bags is a cubic yard of soil?
A cubic yard is 27 cu. ft. — 13.5 bags at 2 cu. ft. or 18 bags at 1.5 cu. ft. Above about one yard, bulk delivery usually beats bags on price.
Do I need to fill the full 12 inches?
Most vegetables root happily in 8–10 inches over open ground. If your bed sits on soil (not concrete), 8 inches of mix over loosened native soil works — that drops this bed to about 11 bags.
Topsoil vs. garden soil vs. raised bed mix?
Bagged “raised bed mix” is pre-blended with compost and costs more per cubic foot; topsoil + your own compost blend is the same result cheaper. Plain fill dirt is neither — don’t plant in it.