Raised Garden Bed Soil Calculator

How to use this raised garden bed soil calculator

The calculator answers one question: how much soil fills the bed you have, or the bed you are about to build. Everything else (bags, cubic yards, liters, cost) is derived from that single volume, so the most useful thing you can do is give it accurate measurements.

1. Measure the inside of the bed. Soil fills the space between the boards, not the footprint on the lawn. A frame built from 1.5 in thick lumber loses 3 in on each axis. If you are still at the planning stage, the lumber cut list generator works out the inside dimensions for you.
2. Enter the depth you will actually fill. If you plan to leave a gap below the top edge, for example so water does not wash soil over the side, enter the depth you will fill rather than the board height.
3. Add filler if you use it. Logs, branches or coarse material at the bottom take up space that you will not buy soil for. The calculator subtracts filler depth before it calculates soil.
4. Choose a settling allowance. The default is 10%, and it is an assumption, not a measurement. More on that below.
5. Read your bag label. Bags are sold by cubic feet, US dry quarts or liters. Pick the unit printed on the bag and the calculator converts it.
6. Type in your own prices. The default prices are placeholders so the comparison has something to show. They are example prices, not market data.

Common bed sizes: soil volume at a glance

The table uses inside dimensions and the same functions as the calculator above. The first column of numbers has no settling allowance; the second adds the 10% assumption so you can see how much it changes the order.

Notice that a 4 × 8 ft bed filled 6 in deep needs the same 16 ft³ as a 4 × 4 ft bed filled 12 in deep. Area and depth trade off one for one, which is why depth is worth deciding before you shop. If you want the answer as a count of bags rather than a volume, the bag count guide has a whole-bag table for the common bag sizes.

Round and L-shaped beds

Not every bed is a rectangle. For a round bed, measure the inside diameter. A 4 ft diameter bed filled 12 in deep holds 12.57 ft³ (that is 4π), which is 9 bags of 1.5 cu ft before any settling allowance.

For an L-shaped bed, measure the two outer arm lengths and the arm width. The calculator splits the L into two rectangles that do not overlap. An L with two 6 ft outer arms and a 2 ft arm width covers 20 ft² (6 × 2 plus 4 × 2), so at 12 in deep it needs 20 ft³.

Deep beds and bottom filler

Tall beds are comfortable to work in, but they hold a lot of soil. A 4 × 8 ft bed filled 24 in deep needs 64 ft³ with no allowance, which is 2.37 cubic yards. If you put 12 in of filler in the bottom, the soil volume drops to 32 ft³ and the calculator reports the filler separately as 32 ft³, so you know how much material to gather for the bottom layer.

Whether filler suits your bed depends on what you grow and how quickly the material breaks down; the calculator only handles the arithmetic. Filler depth must be less than the bed depth, otherwise there is no room left for soil and the tool shows an error instead of a number.

Bagged or bulk soil: compare your own quotes

Once the volume is known, the cost question is mostly about rounding. Bags round up to a whole bag. Bulk soil is usually sold in fixed steps, often with a minimum order and a delivery charge. The calculator applies both rules and shows the cheaper option for the prices you enter. The examples below use made-up quotes to show how the logic behaves; your local prices will differ.

• One 4 × 8 ft bed, 12 in deep, +10%: 35.2 ft³. At an example $8.00 per 1.5 cu ft bag that is 24 bags, or $192.00. Bulk at an example $40.00 per cubic yard rounds up to 1.5 yd³; with an example $50.00 delivery fee the bulk total is $110.00. Under those prices, bags only win below $4.58 per bag.
• One 4 × 4 ft bed, 6 in deep: 8 ft³, or 8 bags of 1 cu ft at an example $6 each ($48.00). Bulk is pushed up to the 1 yd³ minimum order, so it costs $90.00 with delivery. Here bags are cheaper.
• Three 4 × 8 ft beds, 12 in deep, +10%: 105.6 ft³ in total, or 71 bags ($568.00) against 4 yd³ of bulk ($210.00 with delivery).

The pattern is predictable: minimum orders and delivery fees make bulk expensive for small beds, while bag counts grow in step with volume. Where the crossover sits depends entirely on the quotes you collect, which is why the calculator asks for them instead of guessing.

Metric beds

Switch the units to metric and enter centimeters. A 120 × 240 cm bed filled 30 cm deep holds 0.864 m³, or 864 L, which is 30.51 ft³ if your bags are labeled in cubic feet. Centimeters are converted to inches by dividing by 2.54 before any other step, so metric and imperial inputs follow exactly the same formula.

Mixing your own soil

If you blend components, open the custom mix panel and enter a percentage for each one. The percentages must add up to 100. The calculator divides the total volume by those shares and rounds each component up to whole bags on its own. For an equal-parts mix of three components in a 4 × 8 ft bed filled 12 in deep, each component is 10.67 ft³, which is 11 bags of 1 cu ft per component. We do not recommend a particular recipe; the tool simply counts whatever proportions you choose.