How Much Soil for a Raised Bed?
Filling a raised bed takes more soil than people expect, because volume grows fast with depth. An 8-by-4 bed filled 10 inches deep needs over 26 cubic feet — around eighteen bags of the common 1.5-cubic-foot size. The calculator multiplies length by width by depth (converted to feet), then by the number of identical beds, and reports cubic feet, cubic yards, and bag counts.
What to fill it with
Skip filling a whole deep bed with pure bagged "garden soil" — it's expensive and often too dense. A widely used mix is roughly one-third compost for nutrients, one-third topsoil for body, and one-third aeration material like peat moss or coconut coir for drainage. For very deep beds, you can fill the bottom third with coarse organic matter (branches, leaves) and reserve the good mix for the top, where roots live.
Order a little extra
Fresh soil settles noticeably in the first few weeks and after watering, so beds that were full at planting often sink an inch or two. Overfilling slightly at the start saves a second trip. If you're filling several beds or going deeper than about a foot, compare bulk delivery by the cubic yard against bags — the break-even is usually around a cubic yard, or roughly one large 8-by-4 bed.
Frequently asked questions
- How many bags of soil for a 4x8 raised bed?
- At 10 inches deep, about 18 bags of the 1.5-cubic-foot size, or roughly 1 cubic yard in bulk.
- What's the best soil mix for raised beds?
- A common blend is one-third compost, one-third topsoil, and one-third aeration like peat or coir.
- Should I fill the bottom with something cheaper?
- For deep beds, yes — coarse organic matter on the bottom saves money and improves drainage.