How Much Soil Do I Need for a Raised Bed?
The most-asked garden math question, answered with a 30-second formula, ready-made tables and the mix recipe to fill it with.
A standard 4×8 ft bed filled 12 inches deep needs 32 cubic feet of soil — about 1.2 cubic yards, or 16 two-cubic-foot bags. The instant formula: length (ft) × width (ft) × depth (in) ÷ 12 = cubic feet.
The 30-second formula
Soil volume is just the volume of a box. Measure your bed’s inside length and width in feet, decide the fill depth in inches, and run:
length (ft) × width (ft) × depth (in) ÷ 12 = cubic feet
Example: an 8 ft by 4 ft bed filled 12 inches deep → 8 × 4 × 12 ÷ 12 = 32 cubic feet. Divide by 27 for cubic yards (32 ÷ 27 = 1.19 cu yd), and divide by 2 and round up for standard 2 cu ft bags (32 ÷ 2 = 16 bags).
Soil volume tables for common bed sizes
Look yours up — no math required:
| Bed size | Depth | Cubic feet | Cubic yards | 2 cu ft bags |
|---|---|---|---|---|
| 4 × 4 ft | 6 in | 8 | 0.30 | 4 |
| 4 × 4 ft | 12 in | 16 | 0.59 | 8 |
| 3 × 6 ft | 12 in | 18 | 0.67 | 9 |
| 2 × 8 ft | 12 in | 16 | 0.59 | 8 |
| 4 × 8 ft | 6 in | 16 | 0.59 | 8 |
| 4 × 8 ft | 12 in | 32 | 1.19 | 16 |
| 4 × 8 ft | 18 in | 48 | 1.78 | 24 |
Bag counts are rounded up. Add ~10% if you want a settling allowance (see below).
How deep should the soil be?
Depth depends on what you’re growing. Roots need room — but there’s no point paying for 18 inches of premium mix to grow lettuce:
| Crops | Minimum soil depth |
|---|---|
| Salad greens, herbs, radishes | 6–8 in |
| Peppers, bush beans, garlic, onions, beets | 8–10 in |
| Tomatoes, cucumbers, squash, carrots | 12 in |
| Sweet potatoes, parsnips | 12–18 in |
For beds deeper than 12 inches, fill the bottom with cheaper material — bulk topsoil, or logs and branches hügelkultur-style — and reserve the quality mix for the top 8–12 inches where most roots feed.
Skip the tables — calculate your exact bed
Enter your bed’s dimensions for cubic feet, cubic yards, bag count, the 60/30/10 mix and a cost estimate — live, as you type.
The 60/30/10 soil mix
Don’t fill a raised bed with pure topsoil (it compacts) or pure compost (it’s too rich and shrinks). The widely recommended recipe from extension sources is:
| Part | Share | For a 32 cu ft bed | Job |
|---|---|---|---|
| Topsoil | 60% | 19.2 cu ft | Structure and minerals |
| Compost | 30% | 9.6 cu ft | Nutrients and biology |
| Aeration (perlite / rice hulls) | 10% | 3.2 cu ft | Drainage and air |
Bagged “raised bed mix” is essentially this recipe pre-mixed. If you buy components separately, the calculator above works out each part for your bed.
Bags vs bulk: what to buy
Bags (usually 2 cu ft) suit jobs under about 1 cubic yard — easy to carry, exact quantities. Bulk (sold by the cubic yard, tipped on your driveway) is usually cheaper from around 1 cubic yard up, but you’ll need a wheelbarrow and somewhere to put the pile. Around the 1-yard mark, price both.
Don’t forget settling
Freshly filled beds settle — often several inches — as air pockets collapse after the first waterings. Plan for ~10% extra (our calculator has a one-click settling allowance), and top beds back up with an inch or two of compost each season. Settling isn’t soil disappearing; it’s just packing down.
Frequently asked questions
How many bags of soil for a 4×8 raised bed?
At 12 inches deep: 32 cubic feet, i.e. 16 two-cubic-foot bags — 18 if you add the 10% settling allowance. At 6 inches deep, halve it: 16 cu ft, 8 bags.
Can I use just topsoil in a raised bed?
You can, but it compacts and drains poorly on its own. The 60/30/10 mix (topsoil/compost/aeration) is the standard recommendation because it balances structure, nutrients and drainage.
How much does it cost to fill a raised bed?
A 4×8×1 ft bed (32 cu ft) runs roughly $130–$190 in bagged mix or $50–$90 in bulk, depending on your region. Use the calculator’s cost estimate with your local price per cubic foot.
Should the soil go all the way to the top?
Fill to about 1–2 inches below the rim so water doesn’t wash soil over the edge, and leave room for a mulch layer.
Related guides
Best Soil Mix for Raised Beds: The 60/30/10 Recipe Explained
What each part does, what to buy, and what to avoid.
How Deep Should a Raised Bed Be?
Bed depth vs soil depth, and when deeper is just more expensive.
How Much Mulch Do I Need?
The same box math, applied to beds, paths and tree rings.
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