🪴 Soil and mulchFree toolPrintable record
Raised bed soil calculator
Quick answer
Cubic feet of soil = length × width in feet × depth in inches ÷ 12. A 4 x 8 ft bed filled 12 inches deep holds 32 cubic feet. That's 1.19 cubic yards, 22 bags of the 1.5 cu ft size or 16 bags of the 2 cu ft size. Bag sizes vary, so check the number printed on yours.
Source: Miracle-Gro raised bed soil product page, checked October 6, 2026; Kellogg Garden raised bed mix product page, checked October 6, 2026.
Raised bed soil calculator
Change any number and the answer updates as you type.
Soil needed 32 cu ft (1.19 cu yd, 906 liters)
| Buying by | How many |
|---|---|
| 1.5 cu ft bag (40 qt) | 22 bags |
| 2 cu ft bag | 16 bags |
| Bulk, by the cubic yard | 1.19 cu yd |
- Area to cover
- 32 sq ft (3 m²)
- Depth
- 12 in (30.5 cm)
No garden math needed
How to use this, in plain words
Run a tape measure across the inside of the frame, board to board, both ways. The outside measurement includes the boards and overstates the soil.
Decide how deep to fill. For a new bed, that's usually the height of the boards. For a top-up, measure the gap from the soil up to the top of the frame.
Type the length, width and depth into the form. Pick Circle for a round bed or stock tank and use the inside diameter instead.
Find the cubic feet printed on the front of the bag you plan to buy. If it isn't 1.5 or 2, type it into the custom bag field and read your own bag count.
Source: Miracle-Gro raised bed soil product page, checked October 6, 2026; Kellogg Garden raised bed mix product page, checked October 6, 2026.
What the store won't tell you
Before you start
- Measure inside the boards. With boards 1.5 inches thick, a bed that's 4 x 8 ft outside is about 9% smaller inside.
- Bags of the same price can hold different amounts. Check the cubic feet on the bag, not the weight or the quarts alone.
- Round up once, on the total for all your beds, not bed by bed. Leftover bags keep for the top-up next spring.
- New fill settles. Illinois Extension calls settling a fact of raised bed gardening, so plan a top-up rather than overbuying now.
Source: Illinois Extension, refreshing raised bed soil, checked October 6, 2026.
Go deeper: Raised bed soil sank after a month: why, and how much to top up · Bags or bulk: when a cubic yard delivery is cheaper · Inside vs outside: why a 4 x 8 raised bed holds less soil than you think · How many tomato plants fit in a 4 x 8 raised bed · How to fill a tall raised bed without buying 2 yards of soil · Square feet vs cubic feet: how to turn a garden bed into a bag count · Quarts, liters and cubic feet on a soil bag: turning any label into cubic feet
The formula, in words
How it works
- Area of one bed: length × width, in feet. For a round bed: π × radius × radius.
- Volume: area × depth in inches ÷ 12, times the number of beds.
- Cubic yards: cubic feet ÷ 27. A cubic yard is a cube 3 ft on each side.
- Bags: cubic feet ÷ the bag's cubic feet, rounded up to a whole bag. The table uses two sizes that soil makers list on their product pages, 1.5 cu ft and 2 cu ft, and you can add your own.
Source: Miracle-Gro raised bed soil product page, checked October 6, 2026; Kellogg Garden raised bed mix product page, checked October 6, 2026.
Printable sheet
What to record
Next spring, when the bed has settled and needs topping up, you won't have to measure again. The printable soil record has one row per bed:
- Bed name or spot in the yard
- Inside length and width, or diameter
- Depth filled
- Cubic feet and cubic yards
- Bags or yards bought, and the bag size
- Mix or product used
- Date filled and dates topped up
Checked by hand
Worked example
One 4 x 8 ft raised bed, measured inside the boards, filled 12 inches deep.
- Area: 8 × 4 = 32 sq ft.
- Depth: 12 in ÷ 12 = 1 ft. Volume: 32 × 1 = 32 cu ft.
- Cubic yards: 32 ÷ 27 = 1.19 cu yd.
- Bags: 32 ÷ 1.5 = 21.33, so 22 bags of 1.5 cu ft; 32 ÷ 2 = 16, so 16 bags of 2 cu ft.
Why it may not match the bag or the store
If the answer surprises you
❓
The bag's fill guide gives a different count
Makers' fill guides don't agree. Miracle-Gro's puts 3 cubic feet into a space that measures 2 cubic feet, while Kellogg's works out to the plain volume. This tool gives the plain volume and leaves the extra up to you.
Source: Miracle-Gro raised bed soil product page, checked October 6, 2026; Kellogg Garden raised bed mix product page, checked October 6, 2026.
❓
A store calculator says more
Some calculators measure outside the frame or quietly add a margin. Check which measurement they ask for, and whether the result says it includes extra.
❓
The bed looks low a month later
That's settling, not a wrong count. Oregon State Extension says new beds sink as the compost in the mix decomposes. Measure the gap and enter it as the depth to get the top-up.
Source: OSU Extension EM 9308, using compost, checked October 6, 2026.
Other cases
Variants
🟫
Several beds the same size
Enter how many beds you have and the tool multiplies the volume. Round up once, on the total, rather than bed by bed.
⭕
Round beds and stock tanks
Pick Circle and enter the inside diameter. A round bed 4 ft across and 12 inches deep holds 12.57 cubic feet.
🔁
Topping up a settled bed
Measure the gap between the soil and the top of the frame, and enter that as the depth. The result is the top-up alone.
📏
Why makers' fill guides differ
Miracle-Gro's page says two of its 1.5 cu ft bags, 3 cubic feet in all, fill a 2 x 2 ft bed 6 inches deep. That space measures 2 cubic feet. Kellogg's page says one 2 cu ft bag fills a 4 sq ft raised bed, which works out to 6 inches deep with nothing extra. The tool gives the plain volume and leaves any extra for settling up to you.
Source: Miracle-Gro raised bed soil product page, checked October 6, 2026; Kellogg Garden raised bed mix product page, checked October 6, 2026.
Where each figure comes from
Numbers this tool uses
- 1.5 cu ft (40 qt)Raised bed soil bag (Miracle-Gro product page)Miracle-Gro raised bed soil product page, October 6, 2026
- 2.0 cu ft (56.6 L)Raised bed and potting mix bag (Kellogg product page)Kellogg Garden raised bed mix product page, October 6, 2026
- 2 bags fill a 2 x 2 ft bed 6 in deepFill guide on the Miracle-Gro pageMiracle-Gro raised bed soil product page, October 6, 2026
- 1 bag fills a 4 sq ft raised bedFill guide on the Kellogg pageKellogg Garden raised bed mix product page, October 6, 2026
Limitations
- Planning estimate, not a guarantee; check the cubic feet printed on your bag, and measure inside the frame, not the outside of the boards.
- Soil settles after watering. The result is the volume of the space with nothing added for settling.
- Bulk soil is sold by the yard as delivered. Ask the supplier whether they sell part yards before you round up.
What people learn the second year
Tips and tricks
- Write the inside size on the frame. A marker note on the inside of a board saves measuring again next spring when the bed needs a top-up.
- Fill in layers and water between them. Water lightly after every few bags. The mix settles as you go, so you see the real level before the last bags go in.
- Stack the bags by the bed first. Count them against the calculator before you cut any open. It is easier to return a sealed bag than a torn one.
- Cut bags along the long side. Lay the bag flat on the soil, slit the top face and tip it. Less mix spills on the path.
- Use one mix for the whole bed. Mixes differ in texture. One product top to bottom keeps the bed even when it settles.
Read before the store run
Guides that go deeper
🧰 Problem solverRaised bed soil sank after a month: why, and how much to top upWhy raised bed soil settles after filling, what extension services say to add each year, and how to turn the gap into cubic feet and bags.Read the guide 
🧰 Problem solverBags or bulk: when a cubic yard delivery is cheaperHow to compare bagged soil, mulch or compost with a bulk cubic yard: price per cubic foot, the delivery fee, and the bag count where bulk wins.Read the guide 
📘 Know-howInside vs outside: why a 4 x 8 raised bed holds less soil than you thinkA 4 x 8 ft frame of 2x lumber is 93 x 45 inches inside, about 29 square feet of soil. How to measure, what it does to your soil order and your cut list.Read the guide 
📘 Know-howHow many tomato plants fit in a 4 x 8 raised bedAt the extension spacing of 18 to 24 inches, a 4 x 8 ft bed takes 8 to 10 staked tomatoes in two rows, or 4 in wide cages. See the layouts and the math.Read the guide 
🧰 Problem solverHow to fill a tall raised bed without buying 2 yards of soilA 4 x 8 bed 24 inches tall holds 64 cu ft. Put logs, branches and leaves in the lower half and you buy 32 cu ft of soil instead. What goes in, what stays out.Read the guide 
📘 Know-howSquare feet vs cubic feet: how to turn a garden bed into a bag countSquare feet is the bed's footprint; cubic feet adds the depth. Multiply area by depth in feet, divide by the bag size, round up. Worked for a 4 x 8 bed.Read the guide 
📘 Know-howQuarts, liters and cubic feet on a soil bag: turning any label into cubic feetPotting mix comes in quarts, mulch in cubic feet, some bags in liters. How to turn any bag label into cubic feet so you can count bags and compare prices.Read the guide
Common questions
Questions
How many bags of soil does a 4 x 8 raised bed need?
Filled 12 inches deep it holds 32 cubic feet: 22 bags of 1.5 cu ft or 16 bags of 2 cu ft. Filled 6 inches deep it's half that, 16 cubic feet, which is 11 bags of 1.5 cu ft or 8 bags of 2 cu ft.
Source: Miracle-Gro raised bed soil product page, checked October 6, 2026; Kellogg Garden raised bed mix product page, checked October 6, 2026.
How many cubic yards is a 4 x 8 raised bed?
At 12 inches deep the bed holds 32 cubic feet, and 32 ÷ 27 = 1.19 cubic yards.
Do I measure inside or outside the frame?
Inside. With boards 1.5 inches thick, a bed that measures 4 x 8 ft on the outside is 3 ft 9 in x 7 ft 9 in inside, which holds about 9% less soil.
Is bulk soil cheaper than bags?
Compare the price per cubic foot. Divide a bag's price by its cubic feet, and divide the price of a bulk yard by 27. Add any delivery fee to the bulk price first.
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Sources
- Miracle-Gro Organic Raised Bed & Garden Soil, ScottsMiracle-Gro. Checked October 6, 2026.
- Raised Bed & Potting Mix, Kellogg Garden Products. Checked October 6, 2026.
- Refreshing raised bed soil generates exceptional results, University of Illinois Extension. Checked October 6, 2026.
- How to use compost in gardens and landscapes (EM 9308), Oregon State University Extension Service. Checked October 6, 2026.
See every source on the site on the sources page. Spotted an error? Tell us.