Raised Garden Bed Calculator
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Soil, the topsoil and compost split, bags, cost and the boards for the walls, in feet or meters.
Quick answer: To work out the soil for a raised bed, multiply its length, width and depth. A 4 ft by 8 ft bed filled 12 inches deep needs 32 cubic feet, 1.19 cubic yards. Enter your bed size below for the soil in cubic yards, cubic meters or liters, split into topsoil and compost (Penn State Extension recommends 70% soil and 30% compost), plus bags, cost and the boards for the walls. A filler layer for hugelkultur and a settling allowance are optional.
Fill needed
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📐 Formula
Fill = length x width x depth x number of beds x (1 - filler share) x (1 + settling %). In feet and inches, cubic feet = square feet x inches / 12 and cubic yards = cubic feet / 27. In meters, cubic meters = square meters x centimeters / 100 and liters = cubic meters x 1,000. A round bed has area = pi x diameter squared / 4. Each ingredient = fill x its share of the mix. Boards = (2 x (length + width) x layers x beds) / board length, rounded up, where layers = depth / board height, rounded up.
How to Use the Raised Garden Bed Calculator
Choose the units, shape and soil mix
Pick feet and inches or meters and centimeters, rectangle or round, and a soil mix. The first two mixes follow extension advice.
Enter the bed size and the fill depth
Type the length, the width (or diameter) and the depth you will fill to. All three are required.
Add the number of beds, a filler layer and a settling allowance if you want them
All three are optional. Blank means one bed, no filler and no allowance.
Add bag size, prices, board size and weight if you want them
These give a bag count, bagged and bulk costs in your own currency, a board count and a weight.
Read the result
See the fill in cubic yards or cubic meters, the split into topsoil and compost, bags, costs, boards and weight.
How much soil do I need for a raised bed?
The fill for a raised bed is its length times its width times the depth you fill it to. In feet and inches, multiply the three, using the depth in feet (inches divided by 12), to get cubic feet, then divide by 27 for cubic yards. In meters, multiply the three in meters to get cubic meters; one cubic meter is 1,000 liters. This calculator takes the bed size, the number of beds, an optional filler layer and a settling allowance, and then splits the total into topsoil, compost and any third ingredient, so you know what to order. The table shows the fill for common sizes.
| Bed size | 6 in deep | 10 in deep | 12 in deep | 18 in deep |
|---|---|---|---|---|
| 4 x 4 ft | 0.30 (8) | 0.49 (13) | 0.59 (16) | 0.89 (24) |
| 3 x 6 ft | 0.33 (9) | 0.56 (15) | 0.67 (18) | 1.00 (27) |
| 4 x 8 ft | 0.59 (16) | 0.99 (27) | 1.19 (32) | 1.78 (48) |
| 4 x 12 ft | 0.89 (24) | 1.48 (40) | 1.78 (48) | 2.67 (72) |
| 8 x 8 ft | 1.19 (32) | 1.98 (53) | 2.37 (64) | 3.56 (96) |
Worked example: how much soil for a 4x8 raised bed
A bed 4 ft by 8 ft filled 12 inches deep holds 4 x 8 x 1 = 32 cubic feet. Add 10% for settling and the order is 35.2 cubic feet, or 1.30 cubic yards. At 70% soil and 30% compost, that is 24.6 cubic feet of topsoil and 10.6 cubic feet of compost. In 1.5 cubic foot bags, the whole mix is 24 bags (23.5 rounded up). The same bed 10 inches deep is 26.7 cubic feet before settling. Enter 8, 4 and 12, a settling allowance of 10 and the default mix, and the calculator returns the same figures.
Worked example in meters: a 1.2 m by 2.4 m bed
A bed 1.2 m by 2.4 m filled 30 cm deep holds 1.2 x 2.4 x 0.30 = 0.864 cubic meters. With 10% for settling it is 0.950 cubic meters, or 950 liters. At 70% soil and 30% compost that is 665 liters of topsoil and 285 liters of compost, and 24 bags of 40 liters for the whole mix.
The best soil mix for a raised bed
Raised bed soil should drain well and hold organic matter. Penn State Extension recommends a mix of 70% soil and 30% compost for raised beds, and cautions that both must be good quality from reputable sources. Iowa State Extension gives equal parts topsoil, organic matter (well-rotted manure, compost or peat) and coarse sand, and gives about 70% topsoil and 30% compost as another option. A third recipe, 60% topsoil, 30% compost and 10% drainage material, is widely used, but it is not from an extension publication. Choose any of them in the calculator, or enter your own percentages.
| Mix | Share | Source |
|---|---|---|
| Soil and compost | 70% soil, 30% compost | Penn State Extension; Iowa State Extension (about 70% topsoil, about 30% compost) |
| Equal parts | 1/3 topsoil, 1/3 organic matter such as compost, 1/3 coarse sand | Iowa State Extension |
| 60 / 30 / 10 | 60% topsoil, 30% compost, 10% drainage material | A common recipe, not from an extension publication |
Iowa State Extension also advises working the first few inches of the mix into the existing soil underneath, and continuing to add and incorporate until the bed is full, so the bed does not form distinct layers that impede water and roots. Remove any grass sod first.
Raised bed soil calculator in cubic feet, liters and cubic meters
Choose feet and inches for cubic feet and cubic yards, which is how soil is sold in the US and often in Canada. Choose meters and centimeters for liters and cubic meters. A cubic yard is 27 cubic feet, 0.765 cubic meters or 765 liters, and a cubic meter is 1,000 liters or 1.31 cubic yards. Notation such as 8x4x1 means length, width and depth in feet: 8 ft by 4 ft by 1 ft is 32 cubic feet, or 0.9 cubic meters.
Hugelkultur and other filler: how much soil can you save?
A hugelkultur bed starts with a base of decaying wood debris and other compostable material, with soil on top; advocates claim benefits for fertility and water retention, which this calculator does not test. As a volume problem it is simple: the filler layer takes up part of the depth, so you need less soil. Enter the share of the depth the filler occupies. Wood also rots and the mound sinks over the years, so a settling allowance matters more with filler.
Worked example: a 4x8 bed 24 inches deep with a 30% filler layer
Without filler, a 4 ft by 8 ft bed 24 inches deep holds 64 cubic feet of fill, which is 2.37 cubic yards. If the bottom 30% of the depth is logs and branches, the soil is 70% of that: 44.8 cubic feet, 1.66 cubic yards. That saves 0.7 cubic yards of soil. Enter 8, 4 and 24, and 30 for the filler share.
Raised garden bed wood calculator: how many boards?
Enter the board length and height, and the calculator works out how many layers the wall needs, the total length of board and the number of boards. The calculator takes the wall as high as the fill is deep and assumes scraps are reused, so buy one or two spare boards. Board sizes are nominal; the actual size is smaller. In North America the minimum dressed sizes (dry), from NIST PS 20, Table 3, are 1.5 by 5.5 inches for a 2x6, 1.5 by 7.25 inches for a 2x8 and 1.5 by 9.25 inches for a 2x10.
| Board (nominal) | Dressed size (dry) | Layers | Total length | Boards |
|---|---|---|---|---|
| 2 x 6 | 1.5 x 5.5 in (38 x 140 mm) | 3 | 72 ft | 9 |
| 2 x 8 | 1.5 x 7.25 in (38 x 184 mm) | 2 | 48 ft | 6 |
| 2 x 10 | 1.5 x 9.25 in (38 x 235 mm) | 2 | 48 ft | 6 |
Corner posts, screws, brackets and liner are not counted here. Pressure-treated and untreated lumber are different choices with different life spans; check what your supplier and local guidance say for a vegetable bed.
How big should a raised bed be?
Size is a practical choice. Many gardeners keep the width to about 4 feet (1.2 m) so they can reach the middle from either side without stepping on the soil, and use whatever length fits the site. Depth depends on the plants: check each crop's root depth and enter the fill depth you want. Once you know the bed size, the plant spacing calculator shows how many plants fit it, and the garden watering calculator turns the same dimensions into a weekly water figure.
Bagged or bulk soil for a raised bed
Bags are easier to carry and suit small beds. Bulk soil is sold by the cubic yard (US/CA) or cubic meter (UK/AU), and it is cheaper per unit for large beds, but it needs a delivery and somewhere to put the pile. Enter the bag size, the price per bag and the bulk price, and the calculator shows both costs. A cubic yard is 27 one-cubic-foot bags, so divide the bag price by the bag size in cubic feet, then multiply by 27 to compare with a bulk price. Delivery charges are not included.
Using this calculator in the US, UK, Australia and Canada
In the US, soil is sold in bags of 1 to 2 cubic feet and in bulk by the cubic yard, and boards are sold in feet. In Canada both systems are used. In the UK and Australia, bags are labeled in litres and bulk soil is sold by the cubic metre, and timber is sold in metres, so choose metres and centimetres. Words also differ: people say dirt, topsoil or soil for the same fill, and raised bed, planter box or garden box for the same structure. Prices and sizes vary, so you enter your own.
Related garden calculators
For a general soil, compost or mulch count for beds, lawns and pots, use the garden soil calculator. For compost on its own, the compost calculator handles the amount and a browns to greens check. After planting, the planting calendar calculator shows when to sow by zone.
Frequently Asked Questions
Multiply the length, width and depth. A 5 ft by 5 ft bed filled 8 inches deep is 25 x 8 / 12 = 16.7 cubic feet, or 0.62 cubic yards, before any settling allowance. The table above shows common sizes, and the calculator also splits the total into topsoil and compost.
The units matter. In feet, 8x4x1 is 32 cubic feet. Read as meters, 8 x 4 x 1 m is 32 cubic meters, or 32,000 liters, about 35 times as much. Set the units selector to match the notation before you read the result.
The total volume is the same whatever you call it; what changes is the mix. With the default 70 / 30 mix, 70% of the volume is topsoil and 30% is compost. If you fill with one bagged potting or raised-bed mix, choose one soil mix.
Divide the fill in liters by the bag size in liters and round up. A bed 1 m by 1 m filled 20 cm deep is 0.2 cubic meters, or 200 liters, and 220 liters with a 10% settling allowance, which is exactly 11 bags of 20 liters.
A 3 ft by 6 ft bed is 18 square feet. Filled 18 inches (1.5 feet) deep it needs 27 cubic feet, exactly 1 cubic yard. Square feet alone are not enough, because the depth turns an area into a volume.
A round bed shows no board count, because boards are for rectangles; its soil is still worked out from the diameter. For a rectangle, a 4 ft by 8 ft bed with 12 inch walls in 2x6 boards is 3 layers, 72 ft of board and 9 boards of 8 ft.
Divide the thickness of the wood and branch layer by the fill depth and enter the result as a percent. The field accepts 0 to 90. The soil is worked out on what is left, so a larger share means less soil but more settling over the years.
It raises the fill by that percent, so every ingredient, bag count and cost rises with it. In the 4x8 worked example, 10% takes 32 cubic feet to 35.2 and the bag count from 22 bags of 1.5 cubic feet to 24. Leave the field blank for the exact volume.
Extension sources give about 1 inch of water per week as the starting point for a vegetable garden, and the garden watering calculator starts a maturing vegetable bed at 1.5 inches as its own estimate. One inch over one square foot is 144 cubic inches and a gallon is 231 cubic inches, so an inch is about 0.62 gallons per square foot (144 / 231 = 0.6234), and 1.5 inches is about 0.94. Soil type and hot weather change the amount, and the watering calculator adjusts for both.
With example prices in your currency, a 1.5 cubic foot bag at 8 costs 8 / 1.5 x 27 = 144 per cubic yard, against a bulk price of 40.
Enter the number of beds and the calculator multiplies the fill. Two 4 ft by 8 ft beds filled 12 inches deep need 64 cubic feet, 2.37 cubic yards, the same as one 8 x 8 ft bed at that depth.
Sources & Methodology
Soil mix figures come from named extension publications. Penn State Extension, "Soil Health in Raised Beds" gives 70% soil and 30% compost (that page could not be retrieved by automated tools on 2026-10-04, so this figure is quoted from Penn State's search listing, and Iowa State independently gives about 70/30); Iowa State Extension, "What would be a good soil mix for a raised bed?" (read as text on 2026-10-04) gives equal parts topsoil, organic matter and coarse sand, or about 70% topsoil and 30% compost, and advises working the mix into the existing soil. The 60 / 30 / 10 recipe is not from an extension source and is labeled as common. Lumber sizes are nominal. The minimum dressed sizes, dry (19 percent maximum moisture), come from NIST PS 20, the American Softwood Lumber Standard, Table 3: a 2 inch thickness is 1.5 inches, and 6, 8 and 10 inch widths are 5.5, 7.25 and 9.25 inches, read as text on 2026-10-04. The millimeter figures are rounded from the standard's. The hugelkultur description follows Wikipedia's article on Hugelkultur, which notes that the benefits are claimed by advocates.
Volume arithmetic and unit conversions are exact. The board count assumes the wall is as high as the fill is deep and that scraps are reused. Filler share, settling allowance, bag sizes, prices and weights are whatever you enter. Guidance on bed width is common practice and not a standard.