Use this raised bed soil calculator to find how much soil you need for garden beds, planters, and containers — in cubic feet, cubic yards, and bags. Add as many beds as you like, choose a layered fill so you are not paying garden-mix prices for soil nothing will root into, and split a blended recipe into its parts before you order.
Most vegetable roots live in the top 8–12″. Below that the bed only has to drain, so the bottom can be cheap fill, rough compost, or logs.
Bag size, settling & prices — adjust defaults
How much soil for a 4×8 raised bed?
A 4 × 8 ft raised bed filled 12 inches deep needs 32 cubic feet of soil — 1.19 cubic yards, or about 21 bags at 1.5 cu ft. That is the single most asked raised bed question, and the math behind it is simply 4 × 8 × 1 ft. Change the depth and the number moves with it: the same bed at 6″ takes 16 cu ft, at 18″ it takes 48 cu ft. Order 15–20% extra for settling — fresh mix drops noticeably after the first few waterings.
| Bed size | 6″ deep | 12″ deep | 18″ deep | Bags (12″, 1.5 cu ft) |
|---|---|---|---|---|
| 2 × 4 ft | 4 cu ft | 8 cu ft | 12 cu ft | 6 |
| 3 × 6 ft | 9 cu ft | 18 cu ft | 27 cu ft | 12 |
| 4 × 4 ft | 8 cu ft | 16 cu ft | 24 cu ft | 11 |
| 4 × 8 ft | 16 cu ft | 32 cu ft | 48 cu ft | 21 |
| 4 × 12 ft | 24 cu ft | 48 cu ft | 72 cu ft | 32 |
| 5 × 10 ft | 25 cu ft | 50 cu ft | 75 cu ft | 34 |
Bag counts assume 1.5 cu ft bags, the common size for raised bed mixes. At 1 cu ft you need half again as many; at the 0.75 cu ft (40 lb) topsoil size, a 4 × 8 bed at 12″ takes 43 bags. Past roughly 15 bags, bulk delivery usually wins on price even after the fee — and it saves you carrying 43 bags from the car.
Do not fill the whole bed with garden soil
This is the most expensive mistake in raised bed gardening. A 4 × 8 bed at 18″ deep holds 48 cubic feet, and at garden-mix prices that is real money spent on soil nothing will ever root into.
Most vegetable roots live in the top 8–12 inches. Below that the bed only needs to drain and hold moisture, so the bottom can be something cheap:
- Fill dirt or unscreened topsoil — a third to half the price of garden mix
- Rough compost, leaves, grass clippings — free, and it breaks down into good soil
- Logs and branches (hügelkultur) — free, holds water like a sponge, and feeds the bed for years as it rots
Pick a fill strategy in the calculator and it splits the order into good soil and cheap bottom fill, then warns you if the good layer drops below the 6 inches that even shallow-rooted crops need. One caution on hügelkultur: fresh wood pulls nitrogen as it breaks down, so keep it well below the root zone and feed the bed a little harder the first season.
How deep should a raised bed be?
| Depth of good soil | What it grows |
|---|---|
| 6″ | Lettuce, spinach, radishes, herbs — the practical minimum |
| 8–10″ | Beans, peppers, onions, most bush crops |
| 12″ | Tomatoes, squash, carrots, potatoes — the usual target |
| 18″+ | Deep root crops, or beds on concrete with nothing below to root into |
A bed sitting on open ground can be shallower than the numbers above, because roots pass through into the soil underneath. A bed on a patio, deck, or gravel cannot — whatever you put in the box is all the root depth there is. Beds built from stacked wall block rather than lumber are sized the same way, but you will also need a block count and a base — that is what the retaining wall calculator is for.
Blended mixes, split into parts
Few beds get straight topsoil. Common recipes are 60/40 topsoil and compost, 50/50 for richer beds, or the classic Mel’s Mix — equal thirds compost, peat moss or coir, and vermiculite. Ordering these means knowing the volume of each component, not just the total. Choose a blend in the calculator and it breaks the order down by material, in cubic feet and bag counts.
A note on straight topsoil: it compacts badly in a contained box and drains poorly. Use it as part of a blend, not on its own. If you are filling a ground-level area instead of a box, the topsoil calculator handles lawns, grading, and in-ground beds, and it also tells you how much a yard of topsoil weighs before you load a truck.
How to calculate raised bed soil by hand
cubic feet = length (ft) × width (ft) × depth (in) ÷ 12
cubic yards = cubic feet ÷ 27
bags = cubic feet ÷ bag size (cu ft)Worked example: a 4 × 8 ft bed filled 12″ deep. Depth is 12 ÷ 12 = 1 ft. Volume: 4 × 8 × 1 = 32 cubic feet. In yards that is 32 ÷ 27 = 1.19 cubic yards, and at 1.5 cu ft per bag it is 32 ÷ 1.5 = 21 bags. Add 20% for settling and order 38 cu ft, or 26 bags. Measuring the inside of the box matters here — a bed built from 2″ lumber is 3½″ narrower inside than its nominal size. See how many cubic feet are in a cubic yard if you are converting a bulk quote.
FAQ
How much soil for a 4×8 raised bed?
32 cubic feet at 12″ deep — 1.19 cubic yards, or 21 bags at 1.5 cu ft. At 6″ it is 16 cu ft; at 18″ it is 48 cu ft.
How many bags of soil for a raised bed?
Divide cubic feet by the bag size. A 4 × 8 bed at 12″ (32 cu ft) takes 21 bags at 1.5 cu ft, 32 bags at 1 cu ft, or 43 bags at 0.75 cu ft. Past ~15 bags, bulk is usually cheaper.
How deep should a raised bed be?
12″ suits most vegetables. 6″ is the minimum for greens and herbs; 18″ for deep root crops or beds on a hard surface.
Can I fill the bottom of a raised bed with something cheaper?
Yes. Roots live in the top 8–12″, so the bottom can be fill dirt, rough compost, or logs. Keep at least 6″ of good soil on top.
Should I use topsoil in a raised bed?
Only as part of a blend. Straight topsoil compacts and drains poorly in a box — mix it 60/40 or 50/50 with compost.
How much does raised bed soil settle?
15–20% in the first season. Order the extra up front or plan to top the bed up after the first few waterings.