Raised Bed Soil Calculator
Calculate the soil volume to fill a raised bed, split into a topsoil, compost and aeration mix.
What you need
36.8cu ft
Total fill needed — Includes the settling allowance.
- Same amount in cubic yards
- 1.36 cu yd
- 1.5 cu ft bags needed
- 25
- Topsoil / base component
- 22.1 cu ft
- Compost component
- 11 cu ft
- Aeration component (perlite, vermiculite or coarse sand)
- 3.7 cu ft
- Approximate filled weight
- 0.95 US tons
- Growing area
- 32 sq ft
Compare this against bulk delivery pricing.
This is where raised beds get expensive.
Estimates for planning. Confirm quantities with your supplier before ordering — see the assumptions below for the figures used.
Shop this project
The three parts of the mix below are the exact volumes your beds need. Quantities come straight from your calculation above — check them against your supplier's pack sizes before ordering.
Your shopping list
- Topsoil
- 22.1 cu ft
- Compost
- 11 cu ft
- Perlite or vermiculite
- 3.7 cu ft
- Raised bed soil mix
- 36.8 cu ft
- Landscape fabric
- 32 sq ft
Materials
Topsoil
Compost
Perlite or vermiculite
The aeration third of a bed mix — keeps compacted soil draining.
Raised bed soil mix
Prep & extras
Landscape fabric
Blocks weeds under mulch, stone and paver base. Skip it under soil you plan to plant.
Tools & equipment
Wheelbarrow
A 6 cu ft barrow carries roughly 4.5 loads per cubic yard.
Garden rake
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How to use the raised bed soil calculator
Raised beds swallow far more soil than people expect — a 4 by 8 foot bed a foot deep needs about 32 cubic feet, which is over twenty bags. This calculator gives you the total fill volume and splits it into a proven soil recipe, so you can price bulk against bags.
What this calculator assumes
Every estimate depends on figures that vary by supplier and conditions. These are the ones used here, so you can sanity-check the result against your own quote.
- Volume is the inside dimensions of the bed. Measure inside the frame, not the outside of the boards, or you will over-order.
- A 15% settling allowance is included by default. Bagged mixes are fluffed with air and drop noticeably after the first few waterings.
- The bottom-fill option assumes bulky material takes up about a third of the depth. That material rots down over a couple of seasons, so the bed will need topping up.
- Mixed planting soil is taken as roughly 1,400 lb per cubic yard when moist — lighter than plain topsoil because of the compost and aeration content.
- A 1.5 cu ft bag is used for the bag count, the most common size for bagged garden soil. Bulk delivery is usually far cheaper above about 1 cubic yard.
Frequently asked questions
How much soil do I need for a 4x8 raised bed?
A 4 by 8 foot bed 12 inches deep holds 32 cubic feet, which is about 1.2 cubic yards or roughly 21 bags of 1.5 cubic foot soil. At 6 inches deep it halves to 16 cubic feet. This is why bulk delivery wins for anything more than one bed.
What is the best soil mix for a raised bed?
A common and reliable recipe is about 60% topsoil, 30% compost and 10% aeration material such as perlite, vermiculite or coarse sand. The classic Mel's Mix from square-foot gardening is equal thirds compost, peat or coir, and vermiculite. Both work; the topsoil-based mix is cheaper for large volumes.
Can I fill the bottom of a raised bed with something cheaper?
Yes, if the bed is deeper than the plants need. Logs, branches, leaves and cardboard in the bottom third cut your soil cost and eventually break down into good material. Do not do it in a bed under about 12 inches — roots need the depth. Expect the level to sink as the base rots, and plan to top up.
How deep should a raised bed be?
Six inches works for lettuce, herbs and greens if the bed sits on decent soil the roots can reach into. Twelve inches suits most vegetables. Eighteen inches or more for carrots, parsnips and potatoes, or for any bed sitting on concrete or hardpan where roots cannot go deeper.
Should I use potting mix in a raised bed?
No — it is far too expensive at that volume and drains too fast in a large bed. Potting mix is formulated for containers, where drainage is everything. A raised bed behaves much more like ground soil and wants a topsoil-based mix.
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