Raised Bed Soil Calculator
Enter your bed's size and fill height to get the soil volume in cubic feet — and exactly how many bags to buy.
Quick presets:
Measure inside the boards — frame thickness doesn't count.
How the math works
1.5 cu ft bags = cubic feet ÷ 1.5 (round up)
The fill height you actually want is usually 2–4 inches below the top of the boards so water doesn't run straight off — don't fill to the brim. Buy one extra bag beyond the calculated count: soil settles noticeably after the first few waterings, and you'll want it on hand for topping up.
What to fill the bed with
The classic budget blend is roughly 60% topsoil, 30% compost, 10% aeration (perlite, coarse sand, or fine bark). Buying topsoil in bulk and mixing in bagged compost is far cheaper than filling deep beds entirely with bagged "raised bed soil." For very deep beds, the bottom third can be hugelkultur material — logs, branches, leaves — which reduces the soil you need and feeds the bed for years.
FAQ
- Should I put anything on the bottom?
- Cardboard is popular to smother grass and it rots away in weeks. Avoid plastic — raised beds need drainage.
- How much soil for a 4×4 bed?
- At 12 inches deep, 16 cubic feet — about 11 bags of 1.5 cu ft.
- Do raised beds need yearly topping up?
- Yes, expect to add 1–2 inches of compost-rich soil each spring as the level drops.