How this calculator works
A planter is a cylinder or a box. We find the area of its base (π × radius² for round pots, length × width for rectangles), multiply by the soil depth, and divide by 1,728 to convert cubic inches into cubic feet. Potting mix is labelled in dry quarts, at about 25.7 quarts per cubic foot.
Worked example: a 12 inch round pot filled 10 inches deep holds π × 36 × 10 = 1,131 in³, or 0.65 ft³, which is about 16.8 quarts of potting soil.
Potting soil by pot size (round pot, soil 1 inch below the rim)
| Pot diameter | Soil depth | Dry quarts | Cubic feet |
|---|---|---|---|
| 8 in | 6 in | 4.5 | 0.17 |
| 10 in | 8 in | 9.3 | 0.36 |
| 12 in | 10 in | 16.8 | 0.65 |
| 14 in | 11 in | 25.2 | 0.98 |
| 16 in | 13 in | 38.9 | 1.51 |
| 20 in | 16 in | 74.8 | 2.91 |
| 24 in | 20 in | 134.6 | 5.24 |
Tips before you buy
- Use a quality potting mix, not garden soil, in containers. Garden soil compacts, drains poorly and may contain weed seeds and disease.
- Every pot needs drainage holes. A layer of gravel at the bottom does not help drainage, so fill with potting mix and let the water run out.
- In large planters, you can fill the bottom third with empty plastic pots or lightweight filler to save on soil and weight.
- Add slow-release fertilizer to the mix, since nutrients in potting soil run out within weeks of watering.
Tools & materials for this project
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Frequently asked questions
How much soil do I need for a 12 inch pot?
About 17 dry quarts (0.65 ft³) when filled 10 inches deep. A 16 inch pot at 13 inches deep takes about 39 quarts.
How many cubic feet in a quart of potting soil?
One dry quart is 0.039 ft³, so there are about 25.7 dry quarts in a cubic foot.
How many pots will a 2 cubic foot bag fill?
About three 12 inch pots (51 quarts of soil per bag, 17 per pot).
Related calculators & guides
Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.