How deep should a raised bed be

Raised bed height is really two separate questions: how much soil depth your plants need, and how far you want to bend or kneel to reach it. The two do not always point to the same number, which is why beds range from a single course of boards to a waist height box on legs.

The standard 11 inch bed

Two courses of a standard 2x6 board, actual milled height 5.5 inches each, stack to 11 inches, which is the most common raised bed height and the one used throughout the free 4x2 Starter Plan. Eleven inches is enough soil depth for the great majority of vegetables, including tomatoes, peppers, beans, and leafy greens, while keeping the lumber cost and the corner post length reasonable.

When 11 inches is not enough

Root vegetables that grow long and straight, carrots and parsnips in particular, benefit from more depth if the ground underneath the bed is compacted or rocky, since the roots cannot push down past the bed floor into open soil. If the bed sits on reasonably loose native soil, roots can extend below the frame and 11 inches is usually sufficient; on top of a patio, deck, or heavily compacted ground, adding a third course to reach roughly 16 to 17 inches gives those crops room to grow straight.

Going shorter for herbs and shallow crops

A single course at 5.5 inches is workable for herbs, lettuce, and other shallow rooted crops, and uses half the lumber and soil of a two course bed. The tradeoff is less of a barrier against grass and weeds creeping in from the sides, and less soil volume to buffer against drying out between waterings.

Height for comfort: the waist height option

None of the depths above address bending and kneeling. A box lifted on four corner legs, covered in the waist height bed guide, puts the growing surface near waist level, which is a different design problem: it needs a solid bottom panel with drainage holes rather than an open bottom on soil, since it is not sitting on the ground.

How height changes the cut list

Height sets the corner post length directly, since the posts run the full height of the box, and it sets the number of courses, which multiplies the number of long and end wall boards needed. The free configurator recalculates all of this automatically: enter any height from 5.5 to 44 inches and it returns the exact post length, the number of courses, and the resulting board count.

Height and soil volume

Soil volume scales directly with height, so doubling the height roughly doubles the cubic feet of soil needed for the same footprint. A shift from one course to two courses on a 4x2 bed roughly doubles the soil order, which is worth checking with the configurator before committing to a taller design, since soil is usually the single largest cost in building a raised bed once the lumber is bought.

A practical starting point

For a first bed with no specific constraint, 11 inches is a reasonable default: enough depth for nearly everything commonly grown in a home garden, a manageable amount of soil to source and pay for, and a corner post short enough to stay rigid without extra bracing. Adjust up for root crops over compacted ground, or use the waist height design if bending is the main concern.

4 ft by 2 ft Soil Volume by Bed Depth

Use this quick reference for common 2x6 course heights on the 4 ft by 2 ft starter footprint.

2x6 courses	Bed depth	Soil needed
1	5.5 in	3.7 cu ft
2	11 in	7.3 cu ft
3	16.5 in	11.0 cu ft
4	22 in	14.7 cu ft
5	27.5 in	18.3 cu ft
6	33 in	22.0 cu ft
7	38.5 in	25.7 cu ft
8	44 in	29.3 cu ft

Divide cubic feet by 1.5 for standard bag count, or by 27 for cubic yards, and round up before ordering soil.