Guides
How Much Soil for a Raised Garden Bed?
Quick Answer
Multiply bed length by width by height, then multiply by the number of beds and fill level. Divide by 27 for cubic yards or by bag size for bags.
Practical Guide
Raised beds are easier to estimate than irregular landscape beds because the shape is usually rectangular. The key is using the inside dimensions and the actual fill height.
Do not overfill beds. Soil settles after watering, but a small space below the rim helps reduce runoff and keeps mulch or compost from washing out.
Raised Bed Formula
Length feet x width feet x height feet x number of beds x fill level = cubic feet. Cubic feet / 27 = cubic yards.
Example: two beds that are 4 feet by 8 feet by 1 foot at 90% fill need 4 x 8 x 1 x 2 x 0.9 = 57.6 cubic feet, or 2.13 cubic yards.
Simple Soil Mix
A common planning mix is 60% topsoil, 30% compost, and 10% aeration material. Local soil quality and crop needs can change the ideal blend.
| Bed size | Fill height | Approximate volume |
|---|---|---|
| 4 ft x 4 ft | 12 inches | 16 cubic feet |
| 4 ft x 8 ft | 12 inches | 32 cubic feet |
| 3 ft x 6 ft | 18 inches | 27 cubic feet |
FAQ
Should I fill a raised bed to the very top?+
Usually no. Filling to 80% to 90% leaves room for watering, mulch, compost, and settling.
How many bags of soil do I need for a 4 by 8 bed?+
At 12 inches deep, a 4 by 8 bed needs 32 cubic feet. That is 16 two-cubic-foot bags before settling or extra material.
Can I use only topsoil in a raised bed?+
Topsoil alone can compact or drain poorly. Many raised beds perform better with compost and aeration material blended in.
Will raised bed soil settle?+
Yes. Soil often settles after watering and one growing season, so plan for future top-ups.