How to Use This Calculator
- Select your bed shape — rectangular, circular, or L-shaped.
- Enter the dimensions in feet or meters. Use the unit toggle to switch.
- Set the soil depth. Standard raised beds use 6–12 inches of soil.
- Read your results instantly — cubic feet, cubic yards, liters, and number of standard bags.
How Much Soil Does a Raised Bed Need?
A standard 4×8 foot raised bed at 12 inches deep needs about 32 cubic feet of soil — roughly 1.2 cubic yards or 32 one-cubic-foot bags. At 6 inches deep, you need half that: 16 cubic feet.
Most gardeners fill raised beds with a mix of topsoil (60%), compost (30%), and perlite or vermiculite (10%). This calculator gives you the total volume — divide by those percentages to know how much of each amendment to buy.
Common Raised Bed Sizes
| Bed Size | Depth 6" | Depth 10" | Depth 12" |
|---|---|---|---|
| 4 × 4 ft | 8 cu ft | 13.3 cu ft | 16 cu ft |
| 4 × 8 ft | 16 cu ft | 26.7 cu ft | 32 cu ft |
| 3 × 6 ft | 9 cu ft | 15 cu ft | 18 cu ft |
| 2 × 8 ft | 8 cu ft | 13.3 cu ft | 16 cu ft |
Tips to Save Money on Soil
- Buy in bulk — cubic yards from a landscape supply store cost 50–70% less per cubic foot than bagged soil.
- Fill the bottom with logs or cardboard — Hügelkultur style. Reduces the amount of soil you need by 20–30%.
- Mix your own— buying topsoil, compost, and amendments separately is cheaper than pre-mixed "raised bed soil."
FAQ
How deep should a raised bed be?
At minimum 6 inches for shallow-rooted plants (lettuce, herbs). For tomatoes, peppers, and root vegetables, go 10–12 inches. Deeper beds also retain moisture better.
Can I reuse soil from last season?
Yes. Top off with 1–2 inches of fresh compost each season. If soil has compacted significantly, break it up with a garden fork before adding amendments.
What's the difference between topsoil and garden soil?
Topsoil is natural soil screened for debris — dense, good for filling. Garden soil is topsoil amended with compost and nutrients — lighter, better for planting. For raised beds, a mix of both works best.