Potting Soil Calculator
Enter your container’s diameter and fill depth to find how much potting mix you need, in cubic feet and bags.
Measure straight across the widest point.
Adjust depth below if needed.
Covers spillage and compaction. 5–10% is normal.
Everything is calculated in your browser. Nothing you type is sent anywhere or stored.
Bags or bulk delivery?
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Coverage & weight
Material profile
For the default medium container, about 14 inches across, filled 10 inches deep, you’ll need about 0.99 cubic feet of all-purpose potting mix, which is roughly 2 bags (0.5 cu ft each), for about $8 in bulk-equivalent material cost.
Potting mix needed by container size
These estimates use all-purpose potting mix at 1,050 lb per cubic yard with a 5% waste allowance, sized in cubic feet since most potting mix is sold in cubic-foot or quart bags.
| Container | Depth | Mix needed (cu ft) | Bags (0.5 cu ft) |
|---|---|---|---|
| Small pot, 8 in diameter | 8 in | 0.25 cu ft | 1 bag |
| 10 in diameter pot | 8 in | 0.38 cu ft | 1 bag |
| Medium container, 14 in diameter | 10 in | 0.99 cu ft | 2 bags |
| 18 in diameter pot | 12 in | 1.86 cu ft | 4 bags |
| Large planter, 24 in diameter | 14 in | 3.85 cu ft | 8 bags |
| Half whiskey barrel, 30 in diameter | 16 in | 6.87 cu ft | 14 bags |
Potting mix types and drainage
| Type | Weight per yd³ | Best for | Drainage |
|---|---|---|---|
| All-purpose potting mix | 1,050 lb | General container gardening | Excellent |
| Cactus & succulent mix | 1,300 lb | Succulents & cacti | Excellent, low retention |
| Seed-starting mix | 900 lb | Seed trays & propagation | Excellent |
Figures are for dry material. Wet or freshly delivered material can weigh noticeably more.
How to calculate potting soil you need
- Measure the container diameter measure across the inside rim in inches, then convert to feet (divide by 12).
- Set the fill depth 8in for small pots, 10-12in for medium containers, up to 16in+ for large planters and half barrels.
- Find the circular area π × (diameter ÷ 2)², then multiply by fill depth in feet to get cubic feet.
- Add a waste allowance add about 5% to cover settling after the first watering.
- Convert to bags divide total cubic feet by your bag size (commonly 0.5, 1, or 2 cu ft) and round up.
Worked example
Using the calculator’s default medium container, 1.2 ft (about 14 in) diameter, filled 10 inches deep with all-purpose potting mix:
- Radius1.2 ft ÷ 2 = 0.6 ft
- Circular areaπ × 0.6² = 1.13 sq ft
- Depth in feet10 in ÷ 12 = 0.83 ft
- Volume before waste1.13 sq ft × 0.83 ft = 0.94 cu ft
- Plus 5% waste0.94 × 1.05 = 0.99 cu ft
- Cubic yards0.99 ÷ 27 = 0.04 yd³
- Weight (all-purpose mix, 1,050 lb/yd³)0.04 × 1,050 = 38.5 lb
- Bagged option2 bags (0.5 cu ft each) ≈ $8 in bulk-equivalent material cost
Recommended depth by project
| Project | Recommended depth | Notes |
|---|---|---|
| Container type | Typical fill depth | Notes |
| Small pot (6-8 in) | 6-8 in | Herbs, seedlings, and small houseplants |
| Medium container (12-14 in) | 10 in | Most patio pots and mid-size houseplants |
| Large planter (18-20 in) | 12 in | Small shrubs, tomatoes, larger flowering plants |
| Extra-large planter (24 in+) | 14-16 in | Small trees, dwarf fruit trees, large shrubs |
| Half whiskey barrel (28-30 in) | 16 in | Popular for patio vegetables and small trees |
| Seed trays / propagation flats | 1-2 in | Use a fine seed-starting mix, not general potting soil |
Bags or bulk delivery?
Potting soil is sold almost exclusively in bags, since container gardening rarely needs enough volume to justify a bulk delivery. Bulk pricing is shown here only as a reference for comparing cost per cubic foot across brands and mix types.
- Small repairs1-3 bags — a handful of pots or a single medium container; buy off the shelf at any garden center.
- Medium jobs4-15 bags — several containers or a large planter; check for multi-bag discounts at big-box retailers.
- Large jobs15+ bags — many containers or a patio full of planters; compare per-cubic-foot cost against a bulk topsoil-based mix for the largest pots.
Common mistakes
- Using garden soil instead of potting mixgarden soil compacts hard in a container and drains poorly; potting mix is formulated to stay light and aerated in a confined space.
- Filling the container to the brimleave about 1 inch of headspace below the rim so watering doesn’t wash soil over the sides.
- Skipping drainage holescontainers without drainage holes trap water around the roots, even with a well-draining mix — always ensure holes are open and unblocked.
- Reusing old, depleted mix without amendingpotting mix loses structure and nutrients after a season; refresh with 25-50% new mix and compost before replanting.
- Ignoring pot size for root growtha container that’s too small restricts root development and dries out faster; size up as plants mature.
- Adding gravel at the bottom for drainagea gravel layer actually raises the water table inside the pot rather than improving drainage — better to choose a well-draining mix and adequate holes.
What this calculator assumes
Adjust your result if your project differs from these.
- Diameter is measured across the inside of the container at its widest usable point.
- Fill depth stops about 1 inch below the rim to leave room for watering.
- 5% waste covers settling after the first watering.
- Density assumes a standard lightweight potting mix; cactus/succulent mixes with added sand or grit weigh more per cubic yard.
- Bag coverage assumes 0.5 cu ft bags; many retail bags are labeled in quarts (8 dry quarts ≈ 0.31 cu ft).
- Bulk pricing is shown for cost comparison only — most retailers don’t sell potting mix in bulk.
Common questions
How much potting soil do I need?
Find the container’s circular area (π × radius²) and multiply by fill depth in feet. A 14-inch pot filled 10 inches deep needs about 0.99 cubic feet, or 2 bags.
How many quarts are in a cubic foot of potting soil?
About 25.7 dry quarts — so an 8-quart bag is roughly 0.31 cubic feet, and a 16-quart bag is about 0.62 cubic feet.
Can I use garden soil in a pot?
Not recommended — garden soil compacts in containers and drains poorly. Use a purpose-made potting mix formulated for container drainage and aeration.
How much potting mix fills a 24 inch planter?
At a 14-inch fill depth, about 3.85 cubic feet, or roughly 8 bags of 0.5 cu ft each.
Do I need special soil for succulents?
Yes — a fast-draining cactus/succulent mix (sandier, less water-retentive) prevents root rot, unlike standard all-purpose potting mix.
How often should I replace potting soil?
Refresh with 25-50% new mix each growing season, since organic content breaks down and compacts over time, even without repotting.
Why is my potting soil bag measured in quarts, not pounds?
Potting mixes are bulky and lightweight (often peat- or coir-based), so volume (quarts, cubic feet) is a more useful measure than weight for filling a container.
How much does a bag of potting soil weigh?
A standard 0.5 cu ft bag of all-purpose mix weighs roughly 19-20 lb, based on 1,050 lb per cubic yard.
What's the difference between potting mix and seed-starting mix?
Seed-starting mix is finer and lighter (often just peat/coir and perlite, no compost), which helps delicate seedling roots and reduces disease risk.
How much potting soil for a half whiskey barrel planter?
At 16 inches deep, about 6.87 cubic feet, or roughly 14 bags of 0.5 cu ft each — see the reference table above.
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Potting Soil Calculator Estimate
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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.