Landscaping calculator
Raised bed soil calculator: how much soil for a raised bed?
Enter the garden bed size and fill depth to see exactly how much soil a raised bed needs — in cubic feet, cubic yards and bags, broken into the topsoil, compost and aeration parts of a proper raised bed mix.
Your project
The full height of the frame. Most kit beds are 10-18 inches.
Leave 1-2 inches so soil does not wash over the sides when you water.
Branches, leaves or fill dirt in the base cuts the purchased soil — but the bed will settle in year one.
Crews typically order 5-10% extra to cover compaction, spillage and uneven subgrade.
Soil needed
28
cubic feet · includes 5% settling allowance
- Volume in cubic yards
- 1.04 cu yd
- 1.5 cu ft bags
- 19 bags
- Growing area per bed
- 32 sq ft
- Soil depth filled
- 10 in
- Topsoil component (60%)
- 16.8 cu ft
- Compost component (30%)
- 8.4 cu ft
- Aeration component (10%)
- 2.8 cu ft
- Bagged cost
- $152
- Bulk cost
- $62
- Cheaper option
- Bulk delivery
Mix on a tarp rather than layering into the bed. Buying screened topsoil, compost and perlite separately is usually cheaper than a bagged raised bed blend once you pass about one cubic yard.
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How much soil does a raised bed need?
Length times width times fill depth, all in feet, gives cubic feet straight away. A 4 by 8 foot bed with 12 inch sides, filled to 10 inches, needs 4 x 8 x 0.83 = 26.7 cubic feet — just under a cubic yard, or 18 bags at 1.5 cubic feet each.
Fill depth is not bed height. Leave one to two inches below the rim so water and mulch stay inside when you irrigate, and remember soil mounds slightly in the middle as it settles in.
Add about ten percent. Fresh mix is fluffy and drops noticeably after the first few waterings — a bed filled exactly level in April is usually an inch down by June.
The mix that actually grows things
The reliable recipe is roughly 60% screened topsoil, 30% finished compost and 10% aeration material such as perlite, pumice or coarse bark. Topsoil gives the bed body and mineral content, compost gives fertility and biology, and the aeration fraction keeps the whole thing from packing down in a confined box.
Straight compost is the common mistake. It looks perfect on day one, then slumps by half over a season and holds so much water that roots suffocate in wet spells. Straight topsoil is the opposite problem — it compacts into a brick with nowhere to drain.
Bagged potting mix is for containers, not beds. It is peat-based, dries out fast at this volume, and costs three to four times what bulk mix does per cubic yard. Keep it for pots under about three cubic feet.
Filling the bottom, and what it costs you
In a bed taller than about 16 inches, the bottom third can be coarse organic material — branches, leaves, straw, cardboard, old potting soil. Vegetable roots rarely go below 12 inches, so you are only paying for the soil the plants actually use.
The trade-off is settling. That organic layer breaks down over one to two seasons and the bed can drop three or four inches, so plan on topping up each spring. If the bed sits on a patio or deck rather than open ground, skip it — you want drainage material there, not a compost layer.
Bulk beats bags earlier than people expect. Bagged soil works out to roughly $110-$145 per cubic yard equivalent, against $45-$70 for bulk delivered. At two beds — around two cubic yards — bulk is already cheaper even after the delivery fee.
Soil needed for common raised bed sizes
Cubic feet, cubic yards and 1.5 cu ft bags at a 10 inch fill depth.
| Bed size | Cubic feet | Cubic yards | 1.5 cu ft bags |
|---|---|---|---|
| 2 ft x 4 ft | 6.7 | 0.25 | 5 |
| 3 ft x 6 ft | 15 | 0.56 | 10 |
| 4 ft x 4 ft | 13.3 | 0.49 | 9 |
| 4 ft x 8 ft | 26.7 | 0.99 | 18 |
| 4 ft x 12 ft | 40 | 1.48 | 27 |
| 5 ft x 10 ft | 41.7 | 1.54 | 28 |
Bags per cubic yard by bag size
One cubic yard is 27 cubic feet. Round up — nobody sells part bags.
| Bag size | Bags per cubic yard | Bags per 10 cu ft |
|---|---|---|
| 1 cu ft | 27 | 10 |
| 1.5 cu ft | 18 | 7 |
| 2 cu ft | 14 | 5 |
| 3 cu ft | 9 | 4 |
Frequently asked questions
+How much soil do I need for a 4x8 raised bed?
About 32 cubic feet if you fill a 12 inch bed right to the top, or 26.7 cubic feet filled to a more realistic 10 inches. That is roughly one cubic yard, or 18 bags at 1.5 cubic feet.
+How many bags of soil are in a cubic yard?
Twenty-seven 1 cu ft bags, eighteen 1.5 cu ft bags, fourteen 2 cu ft bags or nine 3 cu ft bags. Bagged soil costs two to three times as much per yard as bulk delivered.
+What is the best soil mix for a raised bed?
Roughly 60% screened topsoil, 30% finished compost and 10% aeration material like perlite or coarse bark. Avoid straight compost — it slumps by half in a season — and avoid bagged potting mix, which is built for containers.
+How deep should a raised garden bed be?
Ten to twelve inches suits almost everything, including tomatoes and squash. Root crops like carrots and parsnips want 16 to 18. Beds on a hard surface need the full depth; beds on open soil can be shallower because roots keep going down.
+Can I fill the bottom of a raised bed with something cheaper?
Yes, in beds over about 16 inches. Branches, leaves, straw or old potting soil in the bottom third cuts the purchased soil by a quarter. Expect the bed to settle three to four inches over the first two seasons as that layer breaks down.
+How much does it cost to fill a raised bed?
A 4 by 8 foot bed takes about a cubic yard — roughly $50-$70 bulk delivered, or $120-$150 in bags. Filling four beds at once nearly always justifies a bulk delivery instead.
+Do I need to top up raised bed soil every year?
Add one to two inches of compost each spring. Organic matter burns off and beds drop about an inch a year, faster in the first season and faster still if you filled the base with coarse material.