Buy the soil your bed needs. Skip the guesswork.

Measure the space you will fill

Use the inside length and width, then decide the actual fill depth. Wall height and soil depth may differ. Measure in one consistent system and account for material already in the bed. Do not subtract a buried layer simply because a social post recommends adding one: drainage, root space, and decomposition all need consideration.

Convert the units once

For a rectangular bed, cubic feet equal length in feet multiplied by width in feet multiplied by depth in inches divided by twelve. A four-by-eight-foot bed filled twelve inches deep holds thirty-two cubic feet. Divide by twenty-seven for cubic yards. If bags each contain two cubic feet, that example takes sixteen bags before any extra allowance.

Ask about the material

Topsoil quality varies. Ask the supplier what is in the mix, whether it is intended for a ground-connected raised bed, and what quality or testing information is available. A container with a closed base has different needs from an open-bottom bed. Avoid treating garden soil and container potting mix as interchangeable products.

Plan for settling without over-amending

Use an optional purchase allowance for uneven filling or settling, but understand that it is a shopping estimate. More compost or fertilizer is not automatically better. Soil testing and local recommendations are more useful than repeatedly adding amendments without knowing the starting conditions. Record the supplier and quantity for future top-ups.

Sources & further reading

These extension resources support the growing principles in this guide. Our examples and planning suggestions are editorial explanations. Local recommendations take priority where conditions differ.

• University of Maryland Extension: Soil to fill raised beds ↗

Reviewed September 26, 2026. Read our editorial approach.