Raised bed soil calculator
Enter your bed size and how many beds you're filling. You'll see the total soil, the number of bags, and how much of each ingredient goes into a basic mix.
- Cubic yards
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- 1.5 cu ft bags
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- 2 cu ft bags
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- Topsoil (60%)
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- Compost (30%)
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- Potting mix (10%)
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Mix amounts are in cubic feet. Buy about 10% extra, since new soil settles.
How deep does a raised bed need to be?
| Crops | Soil depth |
|---|---|
| Lettuce, greens, herbs | 6–8 in |
| Most vegetables | 10–12 in |
| Tomatoes, carrots, potatoes | 12–18 in |
If the bed sits on loose ground, roots can grow down past the bottom, so a shallower fill works. If it sits on concrete or compacted clay, fill it deeper.
How the math works
Length times width times depth in feet gives cubic feet. A standard 8 by 4 foot bed filled 12 inches deep holds 32 cubic feet, or about 1.2 cubic yards. That's 22 bags of 1.5 cubic feet.
What soil mix should I use?
A simple, widely used mix is about 60% screened topsoil, 30% compost and 10% potting mix or another light material for drainage. Plain bagged topsoil alone tends to compact in a bed, and pure compost shrinks quickly as it breaks down.
Common questions
Is it cheaper to buy raised bed soil in bulk?
For more than one or two beds, usually yes. One cubic yard is 27 cubic feet, the same as 18 bags of 1.5 cubic feet.
Can I fill the bottom with something cheaper?
In deep beds, many gardeners put untreated logs, branches or leaves at the bottom to cut down on soil. Expect the surface to sink as that material breaks down, and top it up each season.
Why is my bed lower after a few months?
Fresh soil and compost settle and decompose. Losing a couple of inches in the first season is normal, which is why topping up with compost each spring is common.