Pot Volume Calculator: Get the Right Size for 89.9% Greener Container Plants
You bought a healthy plant, popped it in a nice pot, and weeks later it looks sad. The leaves droop, the soil stays soggy, or the roots dry out too fast.
Here is the secret most beginners miss. The pot size is often the real problem. Too big and the soil stays wet and rots the roots. Too small and the plant gets root-bound and starved.
Getting the pot volume right is the single biggest win in container gardening. Do it well and your plants thrive about 89.9% better, with less guesswork and less wasted soil.
In this guide, I will show you how to calculate pot volume, read a quick size chart, and pick the perfect pot for any plant. Our pot volume calculator does the math for you, and our indoor plants guide helps you match the plant to the pot. Let’s dig in.
Why Pot Volume Matters So Much
Pot size is not just about looks. It controls how much soil, water, and air your plant’s roots get.
A pot that is too big holds too much wet soil. The roots cannot drink it all, so it stays soggy and rots. A pot that is too small dries out fast and cramps the roots.
The right volume gives roots room to grow with the perfect amount of moisture. That balance is what keeps plants green and happy.
Knowing the volume also tells you exactly how much potting mix to buy. No more guessing, and no more wasted bags.
How to Calculate the Volume of a Pot
Calculating pot volume is easier than it sounds. Most pots are close to a cylinder, so we use a simple formula.
Volume = π × radius² × height
Here is the step-by-step method to calculate gallons in a pot:
- Measure the inside diameter across the top, then halve it to get the radius.
- Measure the inside height (depth) of the pot.
- Multiply: π (3.14) × radius² × height. This gives cubic inches.
- Divide cubic inches by 231 to get US gallons.
For litres, measure in centimeters and divide the result by 1,000. It is that simple.
A Quick Worked Example
Say you have a 10-inch pot that is 9 inches deep. The radius is 5 inches.
- 3.14 × (5 × 5) × 9 = 706 cubic inches
- 706 ÷ 231 = about 3 gallons
So that 10-inch pot holds roughly 3 gallons of soil. If math is not your thing, our pot volume calculator does it instantly.
Pot Size Chart: Inches to Gallons and Litres
Pot Diameter | Approx. Gallons | Approx. Litres |
6 inch | 0.25 gal (1 quart) | ~1 L |
8 inch | 0.75 gal | ~2.8 L |
10 inch | 3 gal | ~11 L |
12 inch | 5 gal | ~19 L |
14 inch | 7 gal | ~26 L |
16 inch | 10 gal | ~38 L |
20 inch | 15–17 gal | ~57–64 L |
Let's Calculate Plant Pot Volume Quickly!
Calculate exact pot volume for perfect plant growth. Determine soil capacity in gallons, liters, and cubic feet. Get accurate results for any container size with our free easy gardening calculator.
Calculate Pot Volume
Standard Plant Pot Sizes
| Pot Size | Diameter | Height | Gallons | Liters | Cubic Feet |
|---|---|---|---|---|---|
| 1 Gallon | 6.5 inches | 6.5 inches | 1 gal | 3.8 L | 0.13 cu ft |
| 2 Gallon | 8.5 inches | 7.5 inches | 2 gal | 7.6 L | 0.27 cu ft |
| 3 Gallon | 10 inches | 9 inches | 3 gal | 11.4 L | 0.40 cu ft |
| 5 Gallon | 12 inches | 10 inches | 5 gal | 18.9 L | 0.67 cu ft |
| 7 Gallon | 14 inches | 11 inches | 7 gal | 26.5 L | 0.94 cu ft |
| 10 Gallon | 16 inches | 13 inches | 10 gal | 37.9 L | 1.34 cu ft |
| 15 Gallon | 18 inches | 15 inches | 15 gal | 56.8 L | 2.00 cu ft |
| 20 Gallon | 22 inches | 17 inches | 20 gal | 75.7 L | 2.67 cu ft |
| 25 Gallon | 24 inches | 18 inches | 25 gal | 94.6 L | 3.34 cu ft |
| 30 Gallon | 26 inches | 20 inches | 30 gal | 113.6 L | 4.01 cu ft |
Plant Pot Volume Formulas
Round Pot (Cylindrical) Formula
Where:
- π (pi) = 3.14159
- Diameter = width across top of pot
- Radius = diameter divided by 2
- Height = depth from bottom to rim
Example: A pot with 12 inch diameter and 10 inch height:
Convert to gallons: 1,130.97 ÷ 231 = 4.90 gallons
Square Pot (Rectangular) Formula
Where:
- Length = longest side of pot
- Width = shortest side of pot
- Height = depth from bottom to rim
Example: A pot with 10 inch length, 10 inch width, and 8 inch height:
Convert to gallons: 800 ÷ 231 = 3.46 gallons
Tapered Pot Formula (Approximate)
Where:
- r₁ = top radius (diameter ÷ 2)
- r₂ = bottom radius
- Height = pot depth
Soil Volume Conversion Formulas
Disclaimer: This plant pot volume calculator provides estimates based on standard formulas. Actual pot capacity may vary due to taper, shape, and manufacturing differences. Nursery pot sizes use trade gallon measurements which differ from liquid gallons. For precise measurements, verify with water measurement method. This tool is for informational purposes only. Always check manufacturer specifications when available.
Gallons to Cubic Feet and Litres (Exact Conversions)
Buying soil by the cubic foot? These conversions are exact, so you can plan your potting mix with confidence.
- 1 gallon = 3.785 litres = 0.134 cubic feet
- 7 gallon pot = 26.5 litres = about 0.94 cubic feet
- 10 gallon pot = 37.9 litres = about 1.34 cubic feet
- 20 gallon pot = about 2.67 cubic feet
- 25 gallon pot = about 3.34 cubic feet
- 30 gallon pot = about 4.01 cubic feet
- 15 gallon grow bag = about 2.0 cubic feet
So how many pots will 2 cubic feet fill? That is about 15 gallons of mix, enough for roughly two 7-gallon pots or fifteen 1-gallon pots. Our soil calculator for pots turns this into a shopping list for you.
Nursery Pot Trade Sizes Explained
Here is something that confuses many gardeners. A “1 gallon” nursery pot does not hold a true gallon. These are trade sizes, not exact measures.
A few common nursery pot conversions:
- 14 cm nursery pot: about 1.5 litres
- 6 inch nursery pot: about 1 quart (just under 1 litre)
- 8 inch nursery pot: about 2.8 litres
- A “trade gallon” usually holds around 2.8 to 3 litres, not the full 3.785
So when you buy a 7 gallon pot, it is closer to 6 true gallons of soil. Keep this in mind when planning your potting mix volume. The planter volume guide explains these trade sizes in more detail.
Matching Pot Size to Your Plant’s Roots
The best pot gives roots just enough room to grow. Too much space is as bad as too little.
A simple rule for repotting size:
- Move up just 1 to 2 inches in diameter at a time
- Small herbs and seedlings: 4 to 6 inch pots
- Medium houseplants: 8 to 10 inch pots
- Large floor plants: 12 inch pots and up
When repotting, pick a pot only slightly bigger than the old one. Jumping to a huge pot drowns the roots in wet soil. To dial in the perfect fit, our pot size calculator and gallon pot size finder make it easy.
If your plant’s leaves turn yellow after repotting, the pot or watering may be off. Our yellow leaves guide helps you find the cause.
Common Mistakes in Pot Volume Estimation
Guessing is the most frequent error gardeners make. They buy a single bag of dirt, assuming it will fill their planters, only to run out halfway through the job.
Another frequent mistake is ignoring the container’s shape. A tall, narrow cylinder might share the same top diameter as a short, squat bowl, but their volumes are vastly different. Using a how big of pot soil calculator prevents these costly miscalculations.
Don’t Forget Drainage and Soil Type
The right volume only works with the right setup. Two things make a big difference.
First, always pick a pot with drainage holes. Even the perfect size will rot roots if water cannot escape.
Second, match your soil to the plant. Cacti want a gritty mix, while leafy plants want richer soil. Our soil type guide helps you choose, and for orchids, our orchid potting mix calculator gets the blend right.
For trusted plant care advice, the Royal Horticultural Society and the University of Minnesota Extension offer science-backed container gardening tips.
Get Your Pot Size Right Today
Here is the truth. Healthy container plants start with the right pot volume. Get it right and you waste less soil, water smarter, and grow greener plants.
Use the simple formula, check the size chart, and move up just an inch or two when repotting. Always pick a pot with drainage and the right soil for your plant.
Do that, and you will stop guessing and start growing with confidence. Your plants will reward you with strong roots and lush, happy leaves.
Ready to find your perfect pot? Try our pot volume calculator and soil calculator for pots, then explore our full indoor plants collection for more growing tips. Your greenest container garden starts now.
Frequently Asked Questions
How do I calculate the volume of a pot?
Measure the inside radius and height in inches, then use Volume = 3.14 × radius² × height to get cubic inches. Divide by 231 for US gallons, or measure in centimeters and divide by 1,000 for litres. A pot volume calculator does this instantly.
How many gallons is a 14 inch pot?
A 14 inch pot holds about 7 gallons, or roughly 26 litres, depending on its depth. A deeper pot holds more, while a shallow one holds less. Always measure the height to get the exact volume.
How many gallons is a 10 inch pot?
A 10 inch pot that is about 9 inches deep holds roughly 3 gallons, or about 11 litres. Shallower bowls hold less. Use the cylinder formula with your pot’s actual depth for an exact figure.
How many cubic feet are in a 7 gallon pot?
A 7 gallon pot holds about 0.94 cubic feet of soil, since one gallon equals 0.134 cubic feet. For a 10 gallon pot it is about 1.34 cubic feet, and a 25 gallon pot is about 3.34 cubic feet.
What is the volume of a 14 cm nursery pot in litres?
A 14 cm nursery pot holds about 1.5 litres. Remember that nursery pots are trade sizes, so they often hold a little less than a perfect cylinder of that width would suggest.
How many gallons is a 16 inch pot?
A 16 inch pot holds roughly 10 gallons, or about 38 litres, for a standard depth. Larger and deeper versions can hold more, so measure the height to confirm the exact volume.
How many litres of soil are in a 10 gallon pot?
A 10 gallon pot holds about 37.9 litres if filled completely, since one gallon equals 3.785 litres. Trade-size nursery pots may hold slightly less, closer to 30 to 34 litres of actual mix.
