Garden Soil Calculator
Work out how many 1.5 cubic foot bags of garden soil fill your raised bed at your fill depth, plus total cost at your price per bag.
How this calculator works
Garden soil is commonly bought bagged to fill raised beds, so this calculator converts your bed’s volume directly into bag count using a standard 1.5 cubic foot bag size — larger than a typical topsoil bag, since garden soil blends are usually sold in bigger units.
Formula: Cubic yards = (Length ft × Width ft × Depth ft) ÷ 27. Bags = (Cubic yards × 27) ÷ 1.5.
Worked example
An 8 ft × 4 ft raised bed filled 8 inches deep:
- Depth in feet: 8 ÷ 12 = 0.667 ft
- Cubic yards: (8 × 4 × 0.667) ÷ 27 ≈ 0.790 yd³
- Bags: (0.790 × 27) ÷ 1.5 ≈ 14.22 bags
- At $8/bag, that’s $113.78.
Coverage reference
| Bed size | Depth | Bags needed (1.5 cu ft) |
|---|---|---|
| 4 ft × 4 ft | 8 in | ~7.1 bags |
| 8 ft × 4 ft | 8 in | ~14.2 bags |
| 12 ft × 4 ft | 10 in | ~26.7 bags |
How to measure your raised bed
Measure the bed’s inside length and width, not the outer edge of the frame boards, and use the fill depth you actually plan to add soil to — the frame’s full height minus an inch or two of headroom below the rim is typical. For an in-ground garden bed without a frame, measure the tilled or amended area’s footprint instead.
Frequently asked questions
How many bags of garden soil do I need for a raised bed?
This calculator assumes a standard 1.5 cubic foot bag, a common size for bagged garden soil blends. Enter your bed's length, width, and fill depth, and it converts the volume into bag count directly.
What's the difference between garden soil and topsoil?
Garden soil is topsoil that's been amended with compost, aged manure, or other organic matter and blended specifically for planting beds, so it comes ready to grow in. Plain topsoil is closer to unamended native soil — useful for filling and grading, but usually needs compost mixed in before it's ideal for planting.
How deep should a raised bed be filled with garden soil?
8 inches is a workable minimum for most vegetables and annuals in a raised bed. Deep-rooted crops like tomatoes or root vegetables benefit from 10-12 inches, while a bed built primarily for shallow-rooted greens or herbs can get by with 6 inches.
Should I fill a raised bed entirely with garden soil, or mix in something cheaper at the bottom?
Filling the full depth with garden soil is the simplest and most reliable approach for smaller beds. For deeper or larger beds, some gardeners fill the bottom third with cheaper fill material (like coarse woody debris or fill dirt) and reserve the top 8-10 inches for garden soil, which cuts cost but adds settling and drainage variables to manage.
Do I need to add compost on top of bagged garden soil?
Not immediately — bagged garden soil is already amended and ready to plant into. After the first season, though, topping the bed with an inch or two of compost each year replenishes nutrients that plants draw down over a growing season.
Estimates only. Verify quantities with your supplier before purchasing.