Raised bed soil calculator: how much soil to fill your beds
Enter the inside size of your beds, how deep you will fill them and how many there are. Pick a mix and get the cubic feet and the bag count for each ingredient.
Fill to the depth of soil, usually 1 to 2 in below the top board.
Extra for settling
New bed mix settles over the first season. 10% is a sensible top-up allowance.
Soil mix
Bag size (cu ft)
1 bed of 8 × 4 ft at 12 in deep
35.2 cubic feet of soil
1.3 cu yd (32 cu ft before the settling allowance)
| Component | Share | Cu ft | Cu yd | Bags of 1 cu ft |
|---|---|---|---|---|
| Topsoil | 60% | 21.1 | 0.78 | 22 |
| Compost | 30% | 10.6 | 0.39 | 11 |
| Other (perlite, pine bark fines) | 10% | 3.5 | 0.13 | 4 |
| Total | 100% | 35.2 | 1.3 | 37 |
Bags or bulk?
At 1.3 cu yd, bulk from a landscape yard is usually cheaper than bags, even with a delivery fee. Many yards sell a ready-made raised bed blend.
Volume is length × width × depth. Bag counts round up per component.
How the raised bed soil calculator works
The volume of a rectangular bed is length × width × depth. Measure the inside of the frame in feet, convert the soil depth to feet by dividing inches by 12, and multiply. Multiply again by the number of identical beds. Divide cubic feet by 27 for cubic yards, the unit bulk suppliers sell in.
New raised bed mix settles. Compost breaks down, air pockets collapse, and after the first season of watering the level drops. The calculator adds a settling allowance (10 percent by default) so the beds end up full instead of two inches short. Use 0 percent if you are topping up beds that have already settled.
Then the total is split by your mix. Each ingredient's share of the cubic feet is divided by the bag size and rounded up, because you cannot buy part of a bag. The percentages are editable, and if they do not add up to 100 the calculator scales them so the total volume stays right.
- Cubic feet = length (ft) × width (ft) × depth (in) ÷ 12 × number of beds.
- With settling = cubic feet × (1 + allowance %).
- Each ingredient = total × its share; bags = ingredient ÷ bag size, rounded up.
Worked example
Three 4 × 8 foot beds filled 12 inches deep. One bed is 8 × 4 × 1 = 32 cubic feet, so three beds are 96 cubic feet. With 10 percent for settling, buy 105.6 cubic feet, which is 3.9 cubic yards.
With a 60/30/10 mix of topsoil, compost and perlite or pine bark fines, that is 63.4 cubic feet of topsoil, 31.7 of compost and 10.6 of the third ingredient. In 1 cubic foot bags: 64 bags of topsoil, 32 of compost and 11 of the rest, 107 bags in all. At almost 4 cubic yards, a delivered bulk blend is usually the cheaper and easier route.
| Bed size (inside) | Depth | Cubic feet | With 10% settling | 1 cu ft bags |
|---|---|---|---|---|
| 4 × 4 ft | 12 in | 16 | 17.6 | 18 |
| 4 × 8 ft | 12 in | 32 | 35.2 | 36 |
| 4 × 8 ft | 18 in | 48 | 52.8 | 53 |
| 3 × 6 ft | 10 in | 15 | 16.5 | 17 |
| 4 × 12 ft | 12 in | 48 | 52.8 | 53 |
Which soil mix to use
Most raised beds do well with a topsoil-based blend: roughly 60 percent screened topsoil, 30 percent compost and 10 percent something to keep it loose, such as perlite, pumice or fine pine bark. It holds water without staying soggy and is the cheapest to fill in bulk. A 50/50 topsoil and compost blend is the simple version many landscape yards sell premixed as raised bed or garden mix.
Mel's Mix, from the Square Foot Gardening method, is equal parts blended compost, peat moss or coco coir, and coarse vermiculite. It contains no topsoil, is very light and drains well, which suits shallow beds and beds on a deck, but costs more per cubic foot. Do not fill a raised bed with straight bagged potting mix or straight compost: potting mix is expensive at this volume and pure compost slumps and can be too rich.
Saving soil in deep beds
Most vegetables root in the top 12 inches. In beds 24 inches or taller, you can fill the bottom third with logs, branches and leaves (the hugelkultur approach) or coarse fill and put the full soil mix only in the top 12 to 18 inches. Set the calculator depth to the depth of real soil you plan to use. Expect more settling with this method as the wood breaks down.
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Redesign my yard freeFrequently asked questions
How much soil do I need for a 4 × 8 raised bed?⌄
At 12 inches deep, 32 cubic feet, or about 1.2 cubic yards. Add 10 percent for settling and buy around 35 cubic feet: 36 bags of 1 cubic foot or 24 bags of 1.5 cubic feet.
How many bags of soil fill a raised bed?⌄
Divide the bed's volume in cubic feet by the bag size. A 4 × 4 bed 12 inches deep is 16 cubic feet, so 16 bags of 1 cubic foot, 22 bags of 0.75 cubic feet, or 8 bags of 2 cubic feet, before any settling allowance.
What is the best soil mix for raised beds?⌄
A common, inexpensive mix is 60 percent topsoil, 30 percent compost and 10 percent perlite or pine bark fines. Mel's Mix (1/3 compost, 1/3 peat moss or coir, 1/3 vermiculite) is lighter and drains faster but costs more.
Is it cheaper to buy raised bed soil in bags or bulk?⌄
Under about 1 cubic yard (27 cubic feet), bags are usually simpler. Above that, bulk soil from a landscape yard is typically cheaper per cubic foot even with a delivery fee, and many yards sell a premixed raised bed blend.
How deep should soil be in a raised bed?⌄
Twelve inches suits most vegetables and flowers. Root crops like carrots and parsnips prefer 12 to 18 inches. Lettuce, herbs and strawberries manage in 6 to 8 inches.