How Much Soil for a 4×8 Raised Bed?

Project Assumptions

This raised bed example uses a full 12-inch fill depth.

• Raised bed size: 4 ft x 8 ft
• Bed height: 12 inches
• Fill level: 100%
• Bag examples: 1.5 cu ft and 2 cu ft bags
• Simple soil mix example: 60% topsoil, 30% compost, 10% aeration material

Step-by-step Calculation

Volume = length x width x height. Height = 12 inches = 1 ft, so volume = 4 x 8 x 1 = 32 cu ft.

Cubic yards = 32 / 27 = 1.19 cu yd. Two-cubic-foot bags = 32 / 2 = 16 bags. One-and-a-half-cubic-foot bags = 32 / 1.5 = 21.34, so round up to 22 bags.

For a 60/30/10 mix, topsoil = 19.2 cu ft, compost = 9.6 cu ft, and aeration material = 3.2 cu ft.

Practical Buying Notes

Raised bed soil often settles after watering and planting. It is normal to top off the bed later.

Avoid using only heavy garden soil if drainage is poor. A blended mix is usually easier to work with than one dense material.

Common Mistakes

Raised bed estimates should account for height, settling, and bag size.

• Forgetting to convert bed height into feet.
• Buying too little because soil settles.
• Filling the bed with only compost.
• Ignoring drainage.
• Assuming every bag has the same volume.