Fill for one or more raised beds
Soil Calculator for Raised Beds
2 beds, 48 sq ft in all at 12 in deep, need 1.78 cu yd of fill, or 24 bags of 2 cu ft. Choose the crop and the mix below.
Your estimate
1.78 cu yd of fill
48 cu ft across 48 sq ft of 2 beds.
- Bulk orderThe fill, rounded up to the half yard2 cu yd
- Bags of the whole fill2 cu ft per bag, rounded up24 bags
- Topsoil20% of the fill by volume0.36 cu yd
- Organic matter25% of the fill by volume0.44 cu yd
- Other components55% by volume; choose them from a planting guide0.98 cu yd
- Bed 14 × 8 ft at 12 in deep1.19 cu yd
- Bed 24 × 4 ft at 12 in deep0.59 cu yd
The volume is geometry: the beds are filled to their inside depth, before settling. Bags are counted on the whole fill.
How to calculate soil for a raised bed
- Measure each bed inside its frame and multiply length by width. The example has a 4 × 8 ft bed and a 4 × 4 ft bed: 32 + 16 = 48 sq ft.
- Multiply the area by the fill depth in inches and divide by 12: 48 × 12 ÷ 12 = 48 cu ft.
- Divide by 27 for cubic yards: 48 ÷ 27 = 1.78 cu yd. Bulk soil is ordered in half yards, so the order is 2 cu yd.
- Split the fill by volume. Topsoil at 20% is 9.6 cu ft; organic matter at 25% is 12 cu ft; the other 26.4 cu ft is the rest of your mix.
- Divide the whole fill by one bag: 48 ÷ 2 = 24 bags of 2 cu ft.
The fill is geometry: each bed’s inside area times its depth, added up over every bed, before the soil settles. Only the mix split and the bag count depend on your choices.
- Leafy greens on a hard surface
- 8 in or moreUniversity of Maryland Extension, Soil to Fill Raised Beds
- Peppers, tomatoes and squash
- 12–24 inUniversity of Maryland Extension, Soil to Fill Raised Beds
- Shallowest bed Mississippi State gives
- 6 inMississippi State University Extension, Constructing Raised Beds
- Topsoil cap, bed 16 in deep or more
- 20% by volumeUniversity of Maryland Extension, Soil to Fill Raised Beds
- Organic matter by volume
- 25–50%University of Maryland Extension, Soil to Fill Raised Beds
- Bagged soil volumes
- 0.75, 2, 3 cu ftKellogg Garden, All Natural Garden Soil product page (2026); Kellogg Garden, All Natural Garden Soil (Western) product page
Bed depth for each crop
Maryland’s depths are for a bed set on a hard surface, where the roots cannot reach the ground below, and they differ by crop. Illinois gives 6–12 in as the range for root growth in a general vegetable bed. Mississippi State’s minimum is 6 in, and the form flags anything shallower. University of Maryland Extension, Soil to Fill Raised Beds; University of Illinois Extension, Raised Bed Checklist (2016); Mississippi State University Extension, Constructing Raised Beds
| Depth | Cubic feet | Cubic yards | Bags |
|---|---|---|---|
| 6 in | 16 | 0.59 | 8 |
| 8 in | 21.33 | 0.79 | 11 |
| 10 in | 26.67 | 0.99 | 14 |
| 12 in | 32 | 1.19 | 16 |
| 18 in | 48 | 1.78 | 24 |
| 24 in | 64 | 2.37 | 32 |
Mix: topsoil, organic matter and the rest
The form splits the fill by volume. Topsoil is the share you enter, capped at 20% for a bed at least 16 in deep. Organic matter starts at 25%, the low end of Maryland’s 25–50%. Whatever is left is the rest of your mix, which the form leaves to you. University of Maryland Extension, Soil to Fill Raised Beds
Bag sizes come from the bagged garden soil in our data: 0.75 cu ft, 2 cu ft, 3 cu ft. Each bag is counted against the whole fill, not the topsoil share, so the count does not change with the mix. A bag from another brand may print a different volume; enter the figure on that bag.
Where sources disagree
Topsoil share of a raised bed mix
- 20% by volume, the cap for a bed at least 16 in deepUniversity of Maryland Extension, Soil to Fill Raised Beds
- 60% topsoil in one example mix, basis not statedUniversity of Illinois Extension, Raised Bed Checklist (2016)
The form starts at 20%, the cap for a bed at least 16 in deep. Illinois’s example puts 60% topsoil in one mix without saying whether that is by volume or by weight, so the form does not calculate with it.
The shallowest depth for a raised bed
- 6 in, the minimum Mississippi State givesMississippi State University Extension, Constructing Raised Beds
- 6–12 in for a general vegetable bedUniversity of Illinois Extension, Raised Bed Checklist (2016)
- 8 in or more for leafy greens on a hard surfaceUniversity of Maryland Extension, Soil to Fill Raised Beds
The crop sets the depth: 8 in for leafy greens and 12 in for fruiting crops, the low ends of the Maryland ranges. A bed under 6 in is flagged.
Before you order soil for a bed
Measure the inside of the frame once the ground is level. The form gives the volume at the depth you type, before any settling, so add the settling you expect to that depth yourself.
Raised bed soil questions
How deep should a raised bed be for leafy greens?
University of Maryland Extension asks for at least 8 in on a hard surface for leafy greens, beans and cucumbers. Illinois Extension’s general range for a vegetable bed is 6–12 in.
How many bags of soil fill a 4 × 8 ft raised bed?
A 4 × 8 ft bed at 12 in deep holds 32 cu ft. That is 16 bags of 2 cu ft, or 11 bags of 3 cu ft, rounded up to whole bags.
What share of a raised bed mix can be topsoil?
University of Maryland Extension allows topsoil up to 20% by volume in a bed at least 16 in deep, and our data has no topsoil figure for a shallower bed. Illinois’s example mix is 60% topsoil, with its basis left out.
How much organic matter goes in raised bed soil?
Maryland’s target is 25–50% organic matter by volume, or 5–15% by weight. The organic box starts at 25%; the rest of the fill is the other part of your mix, which a planting guide for your area should set.
Is 6 inches deep enough for a raised bed?
6 in is the recommended minimum in Mississippi State’s extension guidance, so a bed that deep meets it. Maryland’s range for peppers, tomatoes and squash starts at 12 in, so those crops need more depth than the minimum.
How do I turn a bed’s size into cubic yards?
Multiply the inside length by the inside width in feet, then by the fill depth in feet, and divide by 27. A 4 × 8 ft bed filled 8 in deep is 21.33 cu ft, or 0.79 cu yd.
Should I order bulk soil or bags for a bed?
For the example, the fill is 1.78 cu yd, so the bulk order is 2 cu yd and the bag count is 24. Bags are the practical choice for one small bed. The cubic yard calculator gives the same volume for a bed of any other shape.
A planning aid, not an engineering calculation: your local code and building inspector have the final word. Terms