Lawn & Garden • Raised Beds • Updated October 29, 2026

How Much Soil for a Raised Bed? Calculator and Chart

Explore related guides: Raised garden bed size · Best raised beds for Iowa · Winterize raised beds · Soil test kits · What to plant in a raised bed in Iowa.

Buying soil for a new raised bed is easy to get wrong: too little and you make a second trip, too much and you have a pile on the driveway. This guide shows how much soil for a raised bed you need, with a calculator, a chart of common bed sizes, and a simple soil mix based on Iowa State University Extension guidance.

How much soil for a raised bed: the short answer

Multiply the inside length × width × depth in feet to get cubic feet. A 4 × 8 ft bed filled 12 inches deep needs 32 cubic feet, about 1.2 cubic yards. That is about 22 bags of 1.5 cubic feet before extra, or about 24 bags if you add 10% for settling.

Raised bed soil calculator

Enter the inside size of your bed and the soil depth you plan to fill. The calculator gives cubic feet, cubic yards, bags and a topsoil and compost split.

Soil chart for common raised bed sizes

Not sure what size to build? See our raised garden bed size guide.

The formula, step by step

1. Measure the inside of the bed, not the outside. Thick boards can take several inches off each side.
2. Convert depth to feet: divide inches by 12. For example, 10 inches is 0.83 ft.
3. Cubic feet = length × width × depth (ft).
4. Cubic yards = cubic feet ÷ 27. Bulk soil is sold by the cubic yard.
5. Bags = cubic feet ÷ bag size. Bags are often 0.75, 1, 1.5 or 2 cubic feet; 1 cubic foot is about 25.7 dry quarts.
6. Add about 10% for settling. New soil sinks after the first few waterings.

Example: a 3 × 6 ft bed, 12 inches deep: 3 × 6 × 1 = 18 cubic feet, or 0.67 cubic yards. With 10% extra, about 20 cubic feet, so 14 bags of 1.5 cubic feet.

What soil mix to use

Iowa State University Extension says raised bed soil should be light and well-drained. It suggests two simple mixes:

• About 70% topsoil and 30% compost. This is the split the calculator uses.
• Equal parts topsoil, organic matter and coarse sand. Organic matter can be well-rotted manure, compost or peat.

ISU Extension also advises making sure brought-in topsoil is not contaminated with soil-borne diseases, lead or pesticides, and that compost is fully mature and not too salty. A soil test after filling tells you whether you need lime or fertilizer.

Bagged soil or bulk soil?

How to fill a raised bed

1. Remove sod where the bed will sit and loosen the soil underneath with a spade or tiller, as ISU Extension recommends.
2. Add a few inches of the mix and work it into the existing soil, so there is no sharp layer between the two.
3. Keep adding and mixing until the bed is full, then water well.
4. Top up after settling. Add more mix after a week or two of watering, then add an inch or two of compost each year.

Tools for filling a raised bed

All four were listed as sold by Amazon.com when checked on October 29, 2026. Check the current listing before you buy.

To measure the bed: STANLEY FATMAX 25 ft Tape

Measure the inside length, width and depth before you order. A rigid blade makes it easy to measure across a bed alone.

To move soil: Gorilla Carts Dump Cart

Moves bulk soil from the driveway to the bed. At 4 cubic feet a load, a 4 × 8 bed takes about eight to nine trips, and the dump feature saves shoveling.

To load and fill: Truper Short D-Handle Shovel

A short handle gives better control when you shovel soil into a bed or loosen the ground underneath.

To mix layers: Spear & Jackson Border Fork

Mixes compost into topsoil and blends each new layer into the soil below, as ISU Extension suggests.

FAQs

How much soil do I need for a 4×8 raised bed?
A 4 x 8 ft bed filled 12 inches deep holds 32 cubic feet, about 1.19 cubic yards. With about 10% extra for settling, that is roughly 24 bags of 1.5 cubic feet or 18 bags of 2 cubic feet.

How do I calculate soil for a raised bed?
Multiply length × width × depth, all in feet, to get cubic feet. Divide cubic feet by 27 to get cubic yards. Divide by the bag size to get the number of bags.

How many bags of soil for a 4×4 raised bed?
A 4 x 4 ft bed 12 inches deep needs 16 cubic feet. With about 10% extra, buy about 12 bags of 1.5 cubic feet or 9 bags of 2 cubic feet.

What soil mix should I use in a raised bed?
Iowa State University Extension suggests about 70% topsoil and 30% compost, or equal parts topsoil, organic matter and coarse sand. Raised bed soil should be light and well-drained.

Is it cheaper to buy bagged or bulk soil?
For one small bed, bags are simpler. Once you need about a cubic yard or more, bulk soil delivered by the yard is usually cheaper per cubic foot. Check local prices and delivery fees.

Do I need to top up raised bed soil?
Yes. Soil settles and compost breaks down, so expect to add an inch or two of compost each year.

Sources and review scope

This guide was prepared on October 29, 2026 from the following sources and from the product listings on Amazon.com. Homingwell did not perform hands-on testing.

• Iowa State University Extension and Outreach – What would be a good soil mix for a raised bed?
• Iowa State University Extension and Outreach – Yard and Garden

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