How Much Soil for a Raised Bed? Cubic Feet, Yards and Bags

By the Mulch Calculator team · Published October 24, 2026 · Facts checked against the sources listed below · About us

Before you order. Results are estimates. Bulk material settles, and loads vary by supplier, so check the bag label or ask your supplier for the real volume and weight. Call 811 before you dig. Keep mulch off tree trunks and away from your house foundation, as UC extension advice explains.

A new raised bed is exciting until you stand in the garden center and stare at the bags. How many do you need? Should you get a truckload instead? On r/gardening, people ask this every spring, often with a photo of an empty frame. The math is the same as for any box, and it takes about a minute.

How much soil for raised bed frames: the short answer

Multiply the inside length, width and depth of the bed in feet. That gives cubic feet. Divide by 27 for cubic yards, or by the bag size for bags. A 4 by 8 foot bed, 1 foot deep, needs 32 cubic feet: about 1.19 yards or 16 bags of 2 cubic feet. Add about 10% for settling.

Step by step

Measure the inside of the frame. Boards take up room, so measure inside them.
Decide the fill depth. It may be less than the frame height if you leave a lip at the top.
Turn everything into feet. Divide inches by 12.
Multiply length x width x depth. That is cubic feet.
Divide by 27 for cubic yards, or by the bag size for bags.
Add a little extra for settling.

Illinois Extension uses this example in its raised bed guide. A bed 6 feet long, 3 feet wide and 1 foot deep holds 6 x 3 x 1 = 18 cubic feet of soil. That is 18 / 27 = 0.67 cubic yards, or 9 bags of 2 cubic feet.

Soil for common bed sizes

Bed size (ft)	Fill depth	Cubic feet	Cubic yards	1 cu ft bags	2 cu ft bags
2 x 4	12 in	8	0.30	8	4
3 x 6	12 in	18	0.67	18	9
4 x 4	12 in	16	0.59	16	8
4 x 8	6 in	16	0.59	16	8
4 x 8	12 in	32	1.19	32	16
4 x 8	18 in	48	1.78	48	24
4 x 12	12 in	48	1.78	48	24
4 x 12	24 in	96	3.56	96	48

These are exact volumes before settling. Round bags up, and add 10% if you want a full bed after the first few waterings.

How deep should the bed be?

Illinois Extension says raised beds are often 6 to 12 inches tall. It suggests 24 inches for gardeners who work from a wheelchair, so they can reach the soil without bending.

Depth has a big effect on cost. A 4 by 8 bed at 6 inches needs 16 cubic feet. At 24 inches it needs 64. If the ground under the bed is decent soil, roots can grow down into it, and a shallower bed may be fine. If you are building on a patio or on hard clay, you may want more depth.

What to fill it with

Illinois Extension suggests a mix of about half compost and half topsoil. So for the 4 by 8 bed at 12 inches, that is about 16 cubic feet of compost and 16 cubic feet of topsoil.

On Ask Extension, a North Carolina gardener needed about 100 cubic feet for four large beds. The expert suggested buying topsoil and compost apart and blending them, so they would know the source of each. The expert also gave a warning. Some sellers blend fill dirt with compost and call it topsoil. A product sold as topsoil that is clearly blended with bark and compost was a red flag to them.

The same expert noted that only a lab test can confirm soil is free of heavy metals. Such tests cost money, but they can give peace of mind for a food garden.

Bags or bulk?

Bags

Bags are easy for one or two small beds. You can carry them, there is no pile on the driveway, and you can mix types. Common sizes are 1, 1.5 and 2 cubic feet. Check the label, since it lists the volume.

Bulk

For several beds, bulk often makes sense. The Ask Extension expert worked out that 100 cubic feet is about 3.7 cubic yards, and suggested ordering about 4.

To compare, turn the bag price into a price per yard:

1 cubic foot bags: price x 27
1.5 cubic foot bags: price x 18
2 cubic foot bags: price x 13.5

Then compare with the bulk price per yard plus delivery.

Weight

Soil is heavy. The Ask Extension expert puts a cubic yard of soil at about 2,000 pounds and compost at about 1,000 pounds. The expert also noted that a standard pickup can carry only about 1,000 pounds without overloading. That is about half a yard of soil, or a full yard of compost. The New Hampshire DES lists finished compost a bit heavier, at 1,400 pounds per yard. Wet material weighs more, so plan for delivery on bigger orders.

Topping up an old bed

Soil in raised beds sinks over time as organic matter breaks down. To top up, measure how far the soil has dropped. Then use that depth in the formula. A 4 by 8 bed that has sunk 2 inches needs 32 x 2 / 12 = 5.3 cubic feet, or 3 bags of 2 cubic feet.

For a thin layer of compost, NC State Extension notes that one cubic yard spread 1 inch deep covers about 324 square feet. That is the same as the math: 27 cubic feet x 12 inches.

Use the calculator

Our topsoil calculator does all of this, with bags, yards and tons. Enter the inside size of the bed and the fill depth. Set the “how many areas” box to the number of beds if they are all the same size. For the general method, see how to calculate cubic yards. If you plan to mulch paths between beds, the mulch calculator and our guide to bags of mulch in a yard can help.

Bottom line

Raised bed soil is length x width x depth in feet. Divide by 27 for yards or by the bag size for bags. A 4 by 8 bed at 12 inches needs 32 cubic feet. Illinois Extension suggests about half compost and half topsoil, with beds 6 to 12 inches tall in most cases. Add a little extra for settling, and plan for the weight.

Tools for this guide

FAQ

How much soil do I need for a 4x8 raised bed?

A 4 by 8 foot bed filled 12 inches deep needs 32 cubic feet, or about 1.19 cubic yards. That is 16 bags of 2 cubic feet. At 6 inches deep, it needs half as much: 16 cubic feet, or 8 bags.

How deep should a raised bed be?

Illinois Extension says raised beds are often 6 to 12 inches tall. It suggests 24 inches for gardeners who work from a wheelchair, so the soil is easier to reach.

What soil should go in a raised bed?

Illinois Extension suggests a mix of about half compost and half topsoil. An Ask Extension expert suggests buying the two apart and blending them yourself, so you know where each came from.

Is it cheaper to buy raised bed soil in bulk?

For bigger beds, often yes, but compare prices near you. Turn the bag price into a price per yard first. For 2 cubic foot bags, multiply the bag price by 13.5. For 1 cubic foot bags, multiply by 27.