Planter Box Soil Calculator
Enter your planter box’s length, width, and fill depth to find the soil volume and number of bags you’ll need to fill it.
Measure straight across the widest point.
Adjust depth below if needed.
Covers spillage and compaction. 5–10% is normal.
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Bags or bulk delivery?
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Coverage & weight
Material profile
For the default 4 ft x 1.5 ft planter box filled 12 inches deep, you’ll need about 0.23 cubic yards (6.3 cubic feet) of raised bed mix, which comes to roughly 13 bags of 0.5 cu ft soil, or about 0.25 tons if ordered in bulk.
Planter box soil needed by box size
These estimates use a raised bed / planter blend at 1,200 lb per cubic yard with a 5% waste allowance for settling.
| Planter box | Depth | Cubic yards | Tons |
|---|---|---|---|
| Window box, 2 ft x 1 ft | 8 in | 0.05 yd³ | 0.031 tons |
| Shallow planter, 3 ft x 1.5 ft | 8 in | 0.12 yd³ | 0.070 tons |
| Standard planter, 4 ft x 1.5 ft | 12 in | 0.23 yd³ | 0.140 tons |
| Long planter, 8 ft x 2 ft | 12 in | 0.62 yd³ | 0.373 tons |
| Deep large planter, 5 ft x 1.5 ft | 18 in | 0.44 yd³ | 0.263 tons |
| Deep vegetable planter, 6 ft x 2 ft | 18 in | 0.70 yd³ | 0.420 tons |
Planter box soil mix types and drainage
| Type | Weight per yd³ | Best for | Drainage |
|---|---|---|---|
| Potting mix (peat/perlite blend) | 1,100 lb | Above-ground planter boxes | Excellent |
| Raised bed / planter blend | 1,200 lb | Deep planter boxes, vegetables | Excellent |
Figures are for dry material. Wet or freshly delivered material can weigh noticeably more.
How to calculate planter box soil you need
- Measure the inside of the box length × width in feet, measured from the interior walls, not the outside footprint.
- Set the fill depth 8in for shallow herb boxes, 12in for a standard planter, 18in for deep-rooted vegetables.
- Convert to cubic yards multiply length × width × depth in feet, divide the cubic-foot volume by 27.
- Add a waste allowance add about 5% to cover settling — soil compacts noticeably in the first few waterings.
- Choose bags or bulk convert cubic feet to bags (commonly 0.5, 1, or 2 cu ft) or order bulk soil by the cubic yard for multiple boxes.
Worked example
Using the calculator’s default 4 ft × 1.5 ft planter box filled 12 inches deep with raised bed / planter blend:
- Area4 ft × 1.5 ft = 6.0 sq ft
- Depth in feet12 in ÷ 12 = 1 ft
- Volume before waste6.0 sq ft × 1 ft = 6.0 cu ft
- Plus 5% waste6.0 × 1.05 = 6.3 cu ft
- Cubic yards6.3 ÷ 27 = 0.23 yd³
- Weight (raised bed blend, 1,200 lb/yd³)0.23 × 1,200 = 280 lb = 0.14 tons
- Order amount (bulk)0.25 tons — rounded to the nearest quarter ton
- Bagged option13 bags (0.5 cu ft each) = about 6.3 cu ft
Recommended depth by project
| Project | Recommended depth | Notes |
|---|---|---|
| Planter use | Recommended depth | Notes |
| Herbs & shallow annuals | 6-8 in | Enough root room for most herbs and bedding flowers |
| Standard flowers & mixed planting | 10-12 in | Good all-purpose depth for most planter box designs |
| Tomatoes & deep-rooted vegetables | 16-18 in | Deeper root run improves yield and reduces watering stress |
| Dwarf fruit trees or shrubs in boxes | 18-24 in | Largest planter boxes; consider a permanent raised bed instead |
| Window boxes | 6-8 in | Limited by box depth; choose shallow-rooted plants |
| Succulents & drought-tolerant mixes | 6-8 in | Add extra drainage material below the soil layer |
Bags or bulk delivery?
A single planter box almost always calls for bagged soil — the volumes are small enough that a bulk delivery minimum and delivery fee rarely make sense unless you’re filling several boxes or a whole row of planters at once.
- Small repairsunder 0.5 ton (about 20 bags) — one or two planter boxes; buy bagged mix from a garden center.
- Medium jobs0.5 to 3 tons — a row of planter boxes or a mix of boxes and containers; compare bulk delivery cost against a bag-load.
- Large jobsover 3 tons — multiple raised planters or a full landscaping project; bulk delivery becomes clearly cheaper per cubic yard.
Common mistakes
- Filling to the very topleave 1-2 inches of headspace below the rim so water doesn’t spill over every time you irrigate.
- Skipping drainage holes or a gravel layerplanter boxes without drainage holes trap water and rot roots — drill holes and consider a thin gravel layer at the base.
- Using plain garden soil instead of a planter mixdense garden soil compacts in a contained box and drains poorly; a lightweight, aerated blend performs far better in planters.
- Ignoring settling after the first wateringsoil compacts noticeably once watered, so top off the box after a week or two rather than assuming the initial fill is final.
- Underestimating box weighta filled planter box can weigh several hundred pounds — check deck or balcony load limits before placing large boxes.
- Forgetting box liners for wood plantersan untreated wood box in direct contact with wet soil rots faster; a breathable liner extends the box’s life.
What this calculator assumes
Adjust your result if your project differs from these.
- Dimensions are the box’s interior length and width, not the outside footprint.
- Fill depth is measured from the bottom of the box to about 1-2 inches below the rim, not to the very top.
- 5% waste covers settling after the first few waterings.
- Density assumes a lightweight raised bed / planter blend; heavier garden soil blends will weigh more per cubic yard.
- Prices are material only; the box itself, liners, and drainage material are separate.
- Bag coverage assumes standard 0.5 cu ft bags; larger 1-2 cu ft bags reduce the bag count proportionally.
Common questions
How much soil do I need for a planter box?
Multiply the box’s length × width × fill depth (in feet) to get cubic feet, then convert to cubic yards or bags. A 4 ft × 1.5 ft box filled 12 inches deep needs about 6.3 cubic feet, or 13 bags.
How many bags of soil fill a planter box?
Depends on bag size — using standard 0.5 cu ft bags, a 6.3 cu ft box needs 13 bags; 1 cu ft bags would need about 7.
What soil is best for planter boxes?
A lightweight raised bed or potting mix blend with good aeration and drainage outperforms dense garden soil, which compacts in a contained space.
How deep should a planter box be for vegetables?
16-18 inches is ideal for tomatoes and other deep-rooted vegetables; 8-10 inches is enough for herbs and shallow annuals.
Should I fill a planter box all the way to the top?
No — leave 1-2 inches of headspace below the rim so watering doesn’t spill soil over the edges.
Do planter boxes need drainage holes?
Yes, always. Without drainage, water pools at the bottom and roots rot, even with a well-draining soil mix.
Can I reuse potting soil from last year in a planter box?
Partially — mix old soil with 25-50% fresh mix and compost, since nutrients and structure break down over a growing season.
How much does a cubic yard of planter mix weigh?
About 1,200 lb for a lightweight raised bed blend, lighter than garden soil or topsoil, which can weigh 2,000+ lb per cubic yard.
Do I need a gravel layer at the bottom of a planter box?
A thin layer of coarse gravel or broken pot pieces over drainage holes can help prevent soil from washing out, though it’s optional with a good soil mix.
How much soil do I need for 5 planter boxes?
Multiply one box’s cubic yardage by 5 — for the default box size that’s about 1.17 cubic yards, or roughly 65 bags.
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Project
| Shape | — |
| Dimensions | — |
| Depth | — |
| Area | — |
| Material | — |
| Waste allowance | — |
Volume & weight (incl. waste)
| Cubic yards | — |
| Cubic feet | — |
| Weight | — |
| Tons (rounded up) | — |
Shopping list
| Bulk order | — |
| Bagged alternative (0.5 cu ft) | — |
| Estimated cost | — |
Notes
Estimate generated by materialcalculate.com. Assumes uniform depth and standard dry material densities. Confirm quantities with your supplier before ordering.