Raised Bed Soil Calculator – Cubic Feet, Yards & Bags

How to use the raised bed soil calculator

Calculate raised bed soil

Raised bed soil settles 10 to 20 percent in its first season, and bagged raised bed mix is usually 1.5 cu ft per bag. Measure the inside of the bed. Estimates only - confirm quantities with your supplier.

Enter the inside length and width of the bed in feet. Standard beds are 8 × 4 ft or 6 × 3 ft.
Enter how deep you will fill it in inches. Most beds are built 10 to 12 inches deep; fill to within an inch or two of the top.
Enter the number of beds, then pick a soil mix if you want the ingredient breakdown.
Read off the total soil in cubic feet, cubic yards and bags. Keep the settling allowance at 10 percent or more: fresh mix sinks noticeably in its first season.

The soil mix: what to fill a raised bed with

Never fill a raised bed with straight garden soil from the ground: it compacts, drains badly and sinks. A proven blend is 60 percent topsoil and 40 percent compost, which feeds plants and holds structure. The other famous recipe is Mel's Mix from square foot gardening: a third compost, a third peat moss or coir and a third perlite or vermiculite. It is fluffy and weed-free but costs more. The calculator breaks your total volume into ingredients for whichever mix you choose.

Soil volume for common bed sizes

Bed size	10 in deep	12 in deep
4 × 4 ft	13.3 cu ft (0.49 yd³)	16 cu ft (0.59 yd³)
6 × 3 ft	15 cu ft (0.56 yd³)	18 cu ft (0.67 yd³)
8 × 4 ft	26.7 cu ft (0.99 yd³)	32 cu ft (1.19 yd³)
10 × 4 ft	33.3 cu ft (1.23 yd³)	40 cu ft (1.48 yd³)

These volumes are before the settling allowance. Bagged raised bed mix usually comes in 1.5 cu ft bags, so an 8 × 4 bed at 10 inches takes about 20 bags, which is why bulk delivery often wins for two beds or more.

Tips for filling raised beds

Fill tall beds (18 in and up) with a base of logs, branches and leaves first (hügelkultur style) and put the good mix on top: it saves money and feeds the soil as it rots.
Water each layer as you fill; dry mix settles unevenly and leaves air pockets.
Top up every spring with an inch or two of compost. The level drops every year as organic matter breaks down.
Line the inside of wooden beds with fabric or plastic to slow rot, but leave the bottom open for drainage and roots.

Frequently Asked Questions

How much soil does an 8 × 4 raised bed hold?

At 10 inches deep, about 26.7 cubic feet, just under 1 cubic yard. At 12 inches deep it is 32 cubic feet (1.19 yd³). Add about 10 percent for settling.

How many bags of soil fill a raised bed?

Bagged mix is usually 1.5 cu ft per bag. An 8 × 4 bed filled 10 inches deep needs about 20 bags; a 4 × 4 bed needs about 10 bags at the same depth.

What is the best soil mix for raised beds?

A 60/40 blend of topsoil and compost suits most vegetables and is affordable in bulk. Mel's Mix (a third each of compost, peat or coir and perlite or vermiculite) is lighter and weed-free, at a higher cost.

Can I fill a raised bed with topsoil only?

You can, but pure topsoil compacts and drains poorly in a bed. Blend in at least a third compost, and add more compost each year as the level drops.

How deep should a raised bed be for vegetables?

Ten to 12 inches of soil suits most vegetables. Root crops like carrots do better with 12 inches or more, and tall beds are easier on your back even if the soil itself is shallower over a filler base.

Why did my raised bed soil level drop?

Fresh mix settles as air pockets collapse and organic matter decomposes: 10 to 20 percent in the first season is normal. That is why the calculator includes a settling allowance, and why beds need a yearly compost top-up.

Should I put anything at the bottom of a deep raised bed?

Yes: logs, branches, straw and leaves (hügelkultur) fill the bottom of beds over about 18 inches deep, with at least 10 to 12 inches of soil mix on top for roots.

Is bagged or bulk soil cheaper for raised beds?

Bulk, once you need more than about half a cubic yard. One 8 × 4 bed is borderline; for two or more beds, a bulk delivery of blended mix usually costs far less than 40 bags.