Plant Pot Volume & Potting Soil Calculator
Measure your pot, set the drainage layer and the space under the rim, and see exactly how much potting soil to buy, in liters, gallons, quarts or cubic feet
Pot Dimensions
Measure the inside of the pot, from the soil side of the wall, not the outer rim
Read the volume printed on the bag. US bags are labeled in dry quarts or cubic feet; European bags in liters.
Estimate based on the inside dimensions you entered. Real pots have thick walls and curved bases, so keep a little extra on hand.
How to use this tool
- Pick the pot shape: tapered round (wider at the top), straight round, or rectangular.
- Measure the inside of the pot and enter the diameters or length and width, plus the height.
- Set the depth of the drainage layer and the space you leave below the rim, then the number of pots.
- Type the volume printed on the bag you plan to buy and read the soil total, the bag count and, if you choose a mix, each component.
Worked example
A tapered pot 25 cm wide at the top, 18 cm at the base and 22 cm tall has a full capacity of 8.1 L. Leaving 2.5 cm below the rim and using no drainage layer, it takes 6.9 L of soil, about 6.2 US dry quarts or 0.24 cubic feet, which is 85% of the full capacity. One 10 L bag covers it with 3.1 L left over.
Methodology
The calculator treats the pot as a simple solid, subtracts the layers that are not soil, and converts the result to the units printed on soil bags.
Six pots, six answers: how much soil each size really takes
Every row uses the tool’s starting setup: 2.5 cm (1 in) of space below the rim and no extra for settling. The last column subtracts a 3 cm layer of clay pebbles at the bottom, which takes a bigger bite out of a small pot than out of a large one. Real pots have thick walls and curved bases, so treat each figure as a close estimate.
| Pot (top × base × height) | Soil (L) | US dry qt | With 3 cm drainage (L) |
|---|---|---|---|
| 12 × 9 × 11 cm | 0.7 | 0.6 | 0.5 |
| 15 × 11 × 14 cm | 1.5 | 1.3 | 1.1 |
| 20 × 14 × 18 cm | 3.4 | 3.1 | 2.9 |
| 25 × 18 × 22 cm | 6.9 | 6.2 | 6.1 |
| 35 × 25 × 30 cm | 19.1 | 17.3 | 17.5 |
| Window box 60 × 20 × 18 cm | 18.6 | 16.9 | 15.0 |
Lena’s six pots. She repots six pots of 20 × 14 × 18 cm with a 3 cm drainage layer, 2.5 cm below the rim and 10% extra for settling. Each takes 3.2 L, so six need 19.0 L, which is 1.9 bags of 10 L: she buys 2 and has almost no spare. The drainage layer adds 3.0 L of clay pebbles in total. If she switches to the airy mix (70% potting mix, 20% perlite, 10% bark), the list becomes 13.3 L of potting mix (1.3 bags, so 2), 3.8 L of perlite and 1.9 L of bark. Bag sizes are your choice here, so match them to the volume printed on the bag. Estimates for planning only.
Potting Essentials
Soil, pots and grow bags that match the volumes you just calculated
Miracle-Gro Indoor Potting Mix for All Plants, 6 qt., 2-Pack
Ready-to-use mix for houseplants that also feeds plants for up to 6 months. Two 6-quart bags per pack.
Plant Pots Indoor with Drainage, 5 Pack Multi-Size Planters Set, White
Five plastic pots in graduated sizes from 4.8 to 7 inches, all with drainage holes. Handy for repotting and for testing volumes.
Gardzen 10-Pack 5 Gallon Grow Bags Fabric Pots with Heavy Duty Handles
Breathable nonwoven fabric pots with handles for vegetables and flowers. A 5-gallon bag holds roughly 19 liters of soil.
As an Amazon Associate we earn from qualifying purchases at no additional cost to you.
Frequently asked questions
How much soil does a pot need if I only know its size in inches? ▼
Enter the inside top diameter, bottom diameter and height in inches after switching to the US units. The calculator handles the cone shape for you, so a pot that is 10 in wide at the top and 7 in at the bottom needs noticeably less soil than a straight 10 in cylinder of the same height.
Should I subtract the drainage layer from the soil volume? ▼
If you put clay pebbles or gravel at the bottom, that space is not filled with soil, so yes. Enter its depth in the drainage field and the result shows the soil and the drainage material as two separate volumes. Leave it at 0 if you do not use one.
Why does the result say bags are rounded up? ▼
You cannot buy part of a bag, so the bag count is rounded up and the unrounded figure is shown below it. If the unrounded number is just above a whole number, consider buying one fewer bag and topping up with a small bag or leftover mix.
How do I convert quarts, gallons and cubic feet of soil? ▼
The result panel shows all of them at once. As a reference, 1 cubic foot is about 28.3 liters, one US dry quart is about 1.1 liters, and one US gallon is about 3.8 liters. Note that bags are labeled in dry quarts, not liquid quarts.
Is a “5-gallon” grow bag really 5 gallons of soil? ▼
Nominal sizes are approximate. A 5-gallon bag is about 19 liters when filled to the brim, but filled to a sensible level with the rim folded or the soil settled, you will use somewhat less. Use the space-below-rim field to match how you actually fill it.