How much soil for a raised bed? Chart by bed size

Quick answer: a 4 x 8 ft raised bed that is 11 in tall (two 2x6 boards) needs about 26.2 cubic feet of soil, or 0.97 cubic yards. That is 19 bags of 1.5 cu ft in a 60/30/10 mix, including 10% extra for settling. The charts below give the same numbers for other common sizes, and every row links to a full plan you can change.

Soil chart for an 11 in tall bed (two 2x6 boards)

Most people build their first bed two 2x6 boards high. Here is how much soil to buy for common sizes, using the planner's default settings: 2x6 walls with 4x4 corner posts, fill to 1 in below the rim, 10%% extra for settling, and the classic 60/30/10 mix. Bag counts round each ingredient up to whole bags.

Soil chart for a 16 1/2 in tall bed (three 2x6 boards)

A taller bed is easier on your back and gives roots more room, but it takes about 55%% more soil than the same bed two boards high.

Costs use the planner's default prices (typical US big-box prices, a bulk price of about $45 per cubic yard and a $75 delivery fee). Prices vary a lot by region and season, so edit them in the planner to match your store.

How we calculate it

Soil volume is inside length times inside width times fill depth. A few details make a real difference:

• Measure inside the walls. A 2x6 is really 1 1/2 in thick, so a 4 x 8 ft bed is about 3 ft 9 in by 7 ft 9 in inside.
• Posts take up room. The planner subtracts each 4x4 post inside the bed.
• Fill to 1 in below the rim, so the soil does not wash over the edge. An 11 in tall bed holds 10 in of soil.
• Add extra for settling (10%% by default).

For the 4 x 8 ft bed, the soil space inside the walls is 23.8 cubic feet. Adding 10% for settling gives 26.2 cubic feet to buy. A simple outside-size estimate (4 x 8 x 10/12) would say 26.7 cubic feet, which is more than the bed holds.

Bags or bulk?

In the charts above, at our default prices, bags were cheaper up to about 22 cubic feet of soil, and bulk delivery was cheaper from about 26 cubic feet (one 4 x 8 ft bed, 11 in tall) and up. Three 4 x 8 ft beds 11 in tall need 78.5 cubic feet (2.91 cubic yards): 54 bags of 1.5 cu ft for about $378, or 3 cubic yards delivered for about $210. Delivery fees vary a lot, so call your local landscape supplier and put their prices into the planner.

Which soil mix?

The planner splits your total into ingredients for three common mixes. For one 4 x 8 ft bed, 11 in tall, in 1.5 cu ft bags:

Extension services suggest similar blends. Iowa State University Extension suggests about 70% topsoil and 30% compost, or equal parts topsoil, organic matter and coarse sand. University of Maryland Extension suggests compost and topsoil in a 1:2 or 1:1 ratio, or compost and a soilless growing mix 1:1. For beds on pavement or concrete, it suggests compost and soilless mix 1:1, with topsoil kept to 20% or less, and only in beds at least 16 in deep. If you buy topsoil in bulk, it recommends asking the supplier for soil test results.

How deep should the soil be?

University of Missouri Extension says most plants need at least a 6 to 12 in rooting zone, and deeper is better. When a bed sits on soil, roots can keep growing into the ground below. University of Maryland Extension says beds on hard surfaces should be at least 8 in deep for leafy greens, beans and cucumbers, and 12 to 24 in deep for peppers, tomatoes and squash. Those beds also dry out faster, so check them often.

These numbers come straight from our planner, which we test on more than 30,000 bed designs. They are estimates for planning. Bag sizes and settling vary, so check product labels and measure your bed before you buy. Spot a problem? Report it.