Potting Soil Calculator
Calculate potting mix for round pots in quarts, liters and cubic feet.
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What this tool does
The Potting Soil Calculator finds how much potting mix fills your containers, treating tapered pots as a frustum (cone with the top cut off) for accuracy, and gives the answer in dry quarts — how most bags are labeled — liters, cubic feet and bags.
How to use the Potting Soil Calculator
- Measure the inside diameter at the top of the pot.
- Enter the depth of soil.
- Enter how many pots of this size.
- Choose straight or tapered.
- Buy the quarts or bags shown.
Formula
V = π × h × (R² + R·r + r²) ÷ 3; quarts = V(in³) ÷ 57.75
- R
- Top radius
- r
- Bottom radius (R for cylinders, 0.75R for tapered)
- h
- Soil depth
- 57.75
- Cubic inches per US liquid quart (bag labels use this)
Worked example
Four 12-inch tapered pots filled 10 inches deep.
Inputs
- Pot diameter (top)12 in
- Soil depth in pot10 in
- Number of pots4
- Pot shapeTapered (bottom ≈ 75% of top)
Result
- Potting mix needed60.4 dry quarts
- Liters57.1 L
- Cubic feet2.02 cu ft
- 1.5 cu ft bags2
Approximate potting mix per pot (tapered)
| Pot size | Quarts |
|---|---|
| 6 in | 1.9 |
| 8 in | 4.6 |
| 10 in | 8.9 |
| 12 in | 15.4 |
| 14 in | 24.5 |
| 16 in | 36.5 |
| 20 in | 71.3 |
Results explained
- Potting mix
- Quarts across all pots.
- Liters
- Metric equivalent.
- Cubic feet
- For larger bags.
- Bags
- Whole 1.5 cu ft bags.
Frequently asked questions
About 9–12 dry quarts for a typical tapered 12-inch pot.
About 25.7 dry quarts per cubic foot by the US liquid quart measure used on bags.
Leave about 1 inch at the top for watering.
No — it raises the water table in the pot. Use a drainage hole instead.
Yes, refresh it with 25–50% new mix or compost and remove old roots.