A Free Tool · Rectangular & Round Beds · Bags or Bulk
How much soil does your raised bed need?
Enter the size of a rectangular or round raised bed and get the volume in cubic feet and
cubic yards, plus how many bags of soil it takes at 1.0, 1.5, or 2.0 cubic feet per bag.
Fill several identical beds at once, and get the one-third Mel's Mix
breakdown if you want to blend your own compost, peat or coir, and vermiculite.
Read this first
These are estimates based on the geometry of your bed, not a substitute for your own
measurements. Buy a little extra — fresh soil and compost-heavy mixes settle as they
break down, so beds usually drop an inch or two in the first season. For more than about a
cubic yard of soil, bagged mix gets expensive and heavy to haul; bulk soil delivered by the
cubic yard is usually cheaper per cubic foot. Check the cubic-foot figure printed on the bag
you buy, since it varies by product.
Pick a bed shape, enter your measurements (length, width, and diameter in feet; fill depth in inches — the way you actually measure), choose a bag size, and you'll get the total soil volume plus bags needed, with an optional Mel's Mix breakdown.
6–8″ for greens & herbs; 10–12″ for most vegetables.
A round bed is treated as a cylinder of soil.
How many identical beds of these dimensions you're filling.
1.5 cu ft is the most common bagged size.
Volume per bed
Total volume (cubic feet)
Total volume (cubic yards)
Bags needed
The math, honestly
How the soil and bag count is figured
It's all volume. For a rectangular bed, the volume in cubic feet is
length × width × depth, with everything in feet — so a
fill depth entered in inches is divided by 12 first. For a round bed,
treat it as a cylinder: π × (diameter/2)² × depth, again
in feet. Multiply by the number of beds for your total.
To convert to cubic yards — the unit bulk soil is sold in —
divide cubic feet by 27 (a cubic yard is 3 ft × 3 ft × 3 ft).
To convert to bags, divide the total cubic feet by the bag size and round
up: ceil(total cu ft ÷ bag size). Bagged soil is sold by the cubic
foot in 1.0, 1.5, and 2.0 cu ft bags, with 1.5 the most common.
Why round up: you can't buy a fraction of a bag, so every bag count is
rounded up to a whole bag. And because fresh soil settles as it breaks down and compacts,
buying a touch extra now saves a second trip to top off later.
Common bed sizes
Worked examples for a few common rectangular beds at three fill depths, computed with the
same formula the calculator uses — so these match what the tool gives you. Bag counts
are for the most common 1.5 cu ft bag size, rounded up to whole bags.
Bed & depth
Cubic feetone bed
Cubic yardsone bed
1.5 cu ft bagsper bed
4 × 4 @ 6″
8.00
0.30
6
4 × 4 @ 10″
13.33
0.49
9
4 × 4 @ 12″
16.00
0.59
11
4 × 8 @ 6″
16.00
0.59
11
4 × 8 @ 10″
26.67
0.99
18
4 × 8 @ 12″
32.00
1.19
22
2 × 8 @ 6″
8.00
0.30
6
2 × 8 @ 10″
13.33
0.49
9
2 × 8 @ 12″
16.00
0.59
11
Cubic feet are length × width × (depth ÷ 12). Cubic yards are cubic feet
÷ 27. Bag counts are cubic feet ÷ 1.5, rounded up. For 1.0 cu ft bags, divide
cubic feet by 1.0; for 2.0 cu ft bags, divide by 2.0 — the calculator does this for you.
Bag sizes and bags per cubic yard
Bagged soil is sold by the cubic foot in three common sizes. Here's how many bags it takes
to make one full cubic yard (27 cubic feet), and how many to fill a standard 4 × 8 bed
filled 10 inches deep (26.67 cubic feet).
Bag size
Bags per cu yd27 cu ft ÷ bag
Bags for 4 × 8 @ 10″26.67 cu ft
1.0 cu ft
27
27
1.5 cu ft
18
18
2.0 cu ft
14
14
Bags-per-yard figures are 27 cu ft divided by the bag size, rounded up to whole bags.
Bagged-soil sizes vary by brand; some raised-bed and potting mixes also come in 1.0, 2.0, or
3.0 cu ft bags. Always check the cubic-foot figure on the bag you buy.
The Mel's Mix one-third breakdown
Mel's Mix, from square-foot gardening, is a popular blend-your-own recipe: equal parts by
volume of compost, peat moss or coconut coir, and coarse vermiculite. The calculator splits
your total into three equal thirds so you know how much of each to buy.
Component
Shareby volume
For 4 × 8 @ 10″26.67 cu ft total
Compost
1/3
8.89 cu ft
Peat moss / coir
1/3
8.89 cu ft
Coarse vermiculite
1/3
8.89 cu ft
Each component is one-third of the total volume (26.67 ÷ 3 ≈ 8.89 cu ft for a
4 × 8 bed at 10 inches). Many gardeners blend several compost types for the compost
third, or swap a quality bagged raised-bed mix for the whole thing — Mel's Mix is a
starting point, not a rule.
Reading the result well
A volume number is only useful if you act on it sensibly. Four things worth knowing before
you buy.
Match depth to what you're growing
Depth drives volume as directly as footprint does. Six to eight inches is plenty for lettuces, greens, and herbs; most vegetables want 10 to 12 inches; deep-rooted crops like tomatoes and carrots do best with 12 inches or more. Going from 6″ to 12″ on the same bed doubles the soil you need, so decide on depth before you price anything.
Plan for settling, and top off each spring
Fresh soil and compost-heavy mixes settle as organic matter breaks down and watering compacts the bed — one to three inches in the first season is normal. Buy a little extra now, and plan to add an inch or two of fresh compost or raised-bed mix every spring. To estimate a top-off, run the calculator with the depth set to the inches you want to add.
Know the bagged-vs-bulk line
Bags are simplest for one or two small beds — no delivery fee, no pile in the driveway. But bags cost more per cubic foot, and a single 4 × 8 bed at 10 inches is already 18 of the 1.5 cu ft bags. Once your total passes about a cubic yard (27 cubic feet), pricing out bulk soil delivered by the cubic yard usually wins on cost, even after the delivery fee.
Buy whole bags — and round up
You can't buy a fraction of a bag, so the calculator rounds every bag count up. Keep an extra bag or two on hand: it's cheap insurance against under-filling, and you'll likely want it for the spring top-off anyway. When you're between two whole-bag counts, round up.
Where to buy
Got your numbers? Here's where to pick up what you need:
The terms behind the calculator, in plain English. These are background definitions for
home gardeners, not horticultural specifications.
Cubic yard
The standard unit for ordering bulk soil — a cube three feet on each side, equal to 27 cubic feet. When you're filling several beds at once, you stop thinking in bags and start thinking in cubic yards, because that's how bulk soil is delivered.
Cubic foot
A cube one foot on each side. It's the working unit for bag math, because bagged soil is sold by the cubic foot. Divide a cubic-foot total by 27 to get cubic yards.
Bag size
How much soil one bag holds, by volume in cubic feet. The common sizes are 1.0, 1.5, and 2.0 cubic feet, with 1.5 the most widely stocked. Bag size is what matters for counting bags — not the bag's weight, which varies with how wet the soil is.
Fill depth
How deep you fill the bed with soil, measured in inches. It's usually given in inches even though length and width are in feet, so the calculator converts it to feet (divides by 12) before computing volume. Depth scales the total directly: doubling the depth doubles the soil.
Bulk soil
Soil batched at a yard and delivered loose by the cubic yard, rather than in bags. It's usually cheaper per cubic foot above about a cubic yard, but comes with a delivery fee and a pile to shovel. Suppliers often have a minimum order.
Mel's Mix
A blend-your-own raised-bed recipe from square-foot gardening: equal parts by volume of compost, peat moss or coconut coir, and coarse vermiculite. The compost feeds plants, the peat or coir holds moisture, and the vermiculite keeps the mix light and well-drained.
Vermiculite
A lightweight mineral, expanded by heat, that holds water and air in the soil and keeps a mix from compacting. Coarse (horticultural) grade is the one used in Mel's Mix; it's the component that makes the blend fluffy and well-drained.
Coconut coir
A fiber made from coconut husks, used as a renewable substitute for peat moss to hold moisture in a soil mix. It often ships as a compressed brick that expands several times its size when wet, so check the expanded cubic feet when estimating how much you need.
Frequently asked
A 4 ft × 8 ft bed filled 10 inches deep needs 4 × 8 × (10/12) = 26.67 cubic feet of soil, about 0.99 cubic yards. That's 18 bags of 1.5 cu ft soil (the most common size), 27 bags of 1.0 cu ft, or 14 bags of 2.0 cu ft. Fill the same bed only 6 inches deep and it drops to 16 cubic feet; at 12 inches it rises to 32. Depth matters as much as footprint. Try your own numbers in the calculator.
Divide the total cubic feet of soil by the size of the bag and round up to whole bags. The most common bagged size is 1.5 cubic feet, with 1.0 and 2.0 cu ft bags also sold. So a bed needing 26.67 cubic feet takes ceil(26.67 ÷ 1.5) = 18 bags of 1.5 cu ft. You can't buy a fraction of a bag, so always round up, and check the cubic-foot figure printed on the bag since it varies by product.
Six to eight inches of soil is enough for shallow-rooted greens, herbs, and lettuces. For most vegetables, 10 to 12 inches gives roots room to develop, and deep-rooted crops like tomatoes and carrots do best with 12 inches or more. If the bed sits on open ground that roots can grow into, you can fill a little less; if it sits on a patio or concrete, fill the full depth.
A popular starting point is Mel's Mix from square-foot gardening: one-third compost, one-third peat moss or coconut coir, and one-third coarse vermiculite, measured by volume. The compost feeds plants, the peat or coir holds moisture, and the vermiculite keeps the mix light and well-drained. Many gardeners adjust the ratio or use a quality bagged raised-bed mix instead; the breakdown above splits your total into equal thirds if you want to build it yourself.
Fresh soil, and especially compost-heavy mixes, settle as organic matter breaks down and the soil compacts with watering. Losing one to three inches in the first season is normal. Plan to top off each spring with an inch or two of fresh compost or raised-bed mix. To estimate the top-off, run the calculator with the depth set to the number of inches you want to add rather than the full bed depth.
For larger volumes, bulk soil delivered by the cubic yard is almost always cheaper per cubic foot than bags, since one cubic yard equals 27 cubic feet — roughly 18 of the 1.5 cu ft bags. The trade-off is a delivery fee, a minimum order, and a pile in your driveway to shovel and cart. For one or two small beds, bags are simpler; once you pass about a cubic yard total, pricing out bulk delivery is usually worth it.
There are 27 cubic feet in one cubic yard. A cubic yard is a cube 3 feet on each side, and 3 × 3 × 3 = 27. Bulk soil is sold by the cubic yard while bagged soil is sold by the cubic foot, so converting your cubic-foot total to cubic yards (divide by 27) tells you how much to order when buying in bulk.
Common mistakes
The volume math is reliable, but these four errors consistently turn a correct calculation
into a soil mix that doesn't perform.
Filling with straight topsoil
Topsoil is screened subsoil — not a raised-bed growing medium. Used alone in a raised bed, it compacts heavily after the first few waterings, destroying the drainage and aeration that make raised beds productive. A good raised-bed mix combines compost, a moisture-retaining component (peat moss or coconut coir), and a material that resists compaction (coarse vermiculite or perlite). University extension programs describe this consistently: straight topsoil alone produces a near-solid block by midsummer.
Not planning for settlement
Compost-heavy mixes settle 1 to 3 inches in the first season as organic matter breaks down and the bed is watered. This is normal — not a sign of a bad mix. Ordering the exact calculated volume and filling to the brim means you'll be adding more soil within a few weeks. Buying a small extra amount on the first fill, or planning an annual spring top-off of an inch or two, is more practical than trying to order the exact minimum.
Confusing cubic feet with cubic yards when calling a supplier
Bulk soil is sold by the cubic yard; bagged soil is labeled in cubic feet. One cubic yard equals 27 cubic feet. If the calculator shows 27 cubic feet and you call the supplier and say "I need 27 yards," you'll be ordering 729 cubic feet — enough for a small farm. Write down both the cubic-foot and cubic-yard figures before calling, and confirm which unit the supplier is quoting. This mistake is more common than it sounds.
Using the same depth for beds on concrete as for beds on open ground
When a raised bed sits on open ground, roots can grow down through the native soil beneath, effectively extending the rooting zone beyond the fill depth. A bed on concrete or patio has no such escape: roots are confined entirely to the fill. Shallow-rooted greens tolerate this fine, but tomatoes, peppers, and most root crops need the full 12 inches (or more) when the bed sits on a hard surface — not a depth you can shave to save a bag.