Potting Soil Calculator
How much potting mix to buy for a set of pots, window boxes, planters or fabric grow bags, in quarts, gallons and the bag sizes stores sell.
A 12 in pot holds about 14 quarts of potting mix; a 5 gallon grow bag about 15 quarts. One cubic foot of potting mix is about 25.7 dry quarts. For a planter box: length × width × depth (in) ÷ 1,728 = cubic feet. Leave about 1 in below the rim for watering.
Potting mix for common pot sizes
| Pot | Quarts | Gallons | Cubic feet |
|---|---|---|---|
| 6 in round (≈5 in tall) | 1.4 | 0.40 | 0.05 |
| 8 in round (≈7 in tall) | 3.7 | 1.06 | 0.14 |
| 10 in round (≈9 in tall) | 7.6 | 2.21 | 0.30 |
| 12 in round (≈11 in tall) | 13.7 | 3.98 | 0.53 |
| 14 in round (≈13 in tall) | 22.4 | 6.50 | 0.87 |
| 16 in round (≈14 in tall) | 31.6 | 9.20 | 1.23 |
| 20 in round (≈18 in tall) | 64.6 | 18.80 | 2.51 |
Grow bags
| Grow bag | Quarts (filled to 90%) | Cubic feet |
|---|---|---|
| 1 gal | 3.1 | 0.12 |
| 3 gal | 9.3 | 0.36 |
| 5 gal | 15.5 | 0.60 |
| 7 gal | 21.7 | 0.84 |
| 10 gal | 30.9 | 1.20 |
| 15 gal | 46.4 | 1.80 |
| 20 gal | 61.9 | 2.41 |
| 25 gal | 77.3 | 3.01 |
Nursery "gallon" pots hold less than a true gallon (a #1 pot is roughly ¾ gal), so measure the pot instead of trusting the label.
Frequently asked questions
How much potting soil do I need for a 12 inch pot?
About 14 quarts (0.53 cu ft) for a typical tapered 12 in pot about 11 in tall, filled to 1 in below the rim. Straight-sided or deeper pots need more.
How many quarts are in a cubic foot of potting soil?
About 25.7 dry quarts. A 2 cu ft bag holds about 51 quarts, and a 1.5 cu ft bag about 39 quarts.
How much soil for a 5 gallon grow bag?
About 15 quarts (0.6 cu ft) when filled to about 90%, which leaves room for watering and settling.
How do I calculate soil for a planter box?
Multiply length × width × soil depth in inches and divide by 1,728 for cubic feet, then multiply by 25.7 for quarts. A 36 × 10 × 9 in box needs about 1.9 cu ft, or 48 quarts.
Can I use garden soil in pots?
Not on its own: it compacts and drains poorly in containers. Use a peat- or coir-based potting mix, and add perlite for drainage-hungry plants such as succulents and herbs.
Run a garden club, nursery or landscaping site? Embed this calculator free with one line of code.
Related free tools
Raised Bed Soil Calculator
Soil and mix ingredients for raised beds, in cu ft, yards and bags.
Open tool →Topsoil Calculator
Cubic yards, tons, bags and truckloads of topsoil for lawns, beds and gardens.
Open tool →Fertilizer Calculator
Pounds or ounces of any N-P-K fertilizer per 1,000 sq ft and for your whole lawn.
Open tool →Sod Calculator
Square feet, pallets, slabs or rolls, topsoil and cost for any lawn shape.
Open tool →Sources and assumptions
Round pots are treated as tapered (base 80% of the rim diameter) and filled to 1 in below the rim; planters to 1 in below the top; grow bags to 90%. 1 cu ft = 1,728 cu in = 25.714 U.S. dry quarts; 1 gallon = 231 cu in.