plant pot sizes inches to gallons

Translation please – Pot diameter (inches) to gallons)

So often one or the other is mentioned but rarely both. It would be handy to have this info.

Comments (9)

greenman28 NorCal 7b/8a

Are you talking about plastic nursery pots?

I just measured a one-gallon black plastic nursery pot, and the top diameter is 6.5 inches.

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It’s difficult to assign a volume based on pot diameter because both the depth and the shape of the container play heavily into the determination. E.g., a truncated cone has less volume than a cylinder of the same (opening) diameter ht., and a 12″ deep container with a given diameter will hold twice as much soil as a 6″ deep container with the same diameter.

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Measuring straight sided tapering pots in inches: the area (pi or 3.142 x radius squared) of the top + the area of the bottom divided by 2 and then multiplied by the height gives you the volume in cubic inches. Divided by 1728 gives cubic feet. I cubic foot = 7.48 US gallons.

A quicker way: (Diameter top + Diameter bottom divided by 4) squared. then multiply by the height by 0.0136 = volume in US gallons.
(For volume in liters multiply height by 0.051)

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I should have said roughly speaking. Like a 16″ pot is like 3 gallons? Now that is a off the top of my head guess. Probably all wrong. But I’m just looking for ball park sizes. And recognizing that shape has a lot to do with it. Anyway thanks all.

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Take 1/2 of the diameter and multiply it by itself, then multiply that answer by 3. In this case half of 16 is 8 – 8×8=64 64×3=192. This roughly gives you the surface area of the container opening. To get the volume, multiply by the ht of the container. Let’s say the container is 10″ deep. 192×10= 1,920 cubic inches for the volume. To convert cubic inches to (liquid measure) gallons, divide by 230. so 1,920 divided by 230= 8-1/3 gallons. That would be for a container with straight sides, For tapered nursery containers, deduct about 25% of the volume of containers with straight sides, so a tapered container would hold closer to 6 gallons.

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Thanks Al. I will make my own table for various common sizes.

Next I need to consult with rose people on their experiences with potting different types of roses.

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gardengal48 (PNW Z8/9)

Be careful making comparisons with nursery containers and volumes. For reasons known only to the nursery industry, labled volumes do not necessarily match actual volume. For example, a standard #1 round black nursery pot, known as a “trade” gallon, holds only 3 quarts of soil.

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calistoga_al ca 15 usda 9

Thanks gardengal, math makes me dizzy. For those of us who can remember the pre-plastic days with the straight sided metal cans that every can had to be cut down the side to get the plant out, who longs for the good old days? A one gallon metal can was able to hold one gallon liquid and so they were referred as “one gallon containers”. When Plastic pots were made with a taper that allowed the plant to slip out, the pots to be able to stack together, we were all so grateful, who cared that they no longer held a gallon. Someone filed a complaint a few years ago with the weight and measures people that they were paying for a one gallon measure that was not “one gallon”. Now you will notice they refer to them as “trade one gallon”, thus avoiding the claim of “not containing one gallon”. Al

So often one or the other is mentioned but rarely both. It would be handy to have this info.

Container and Pot Sizes: How Much Soil Do I Need?

Container and growing pots come in a variety of sizes. In the United States nursery and garden centers sell pots by the size in inches and gallons. In the United Kingdom, Europe, and most of the rest of the world containers are sold by the size in centimeters and liters.

There are few standards when it comes to container sizes and volumes. To determine the size of a pot measure across the top from one side to the other to determine how many inches or centimeters it is. However, because some pots are long and others are squat and because the sides of some pots are straight and others are tapered, the volume can vary.

How Much Soil Does a Container Need

When it comes to filling a pot with soil estimating how much soil you need is an approximation. Often the volume of a container is measured in liquid quarts or liters, but, of course, when you purchase soil you are purchasing dry (potting soil is not liquid). A dry quart is equal to about 1⅛ liquid quarts. When deciding how much soil to purchase it’s best to factor soil compression that commonly results from moistening and pressing the soil into the pot. Soil compression can add another 15 to 20 percent dry soil to the container. Also take into consideration that when you transplant a plant from one container to another, you will be moving some soil around the roots of the plant.

Take notes on the pots you have and the soil they require. In short order, you will have a realistic estimate of how much soil you will need to purchase when potting plants.

Container garden on a balcony

Soil for Standard Clay Pots and Plastic Nursery Pots:

This chart will help you translate container sizes for standard clay pots and black nursery pots and give you an approximation of how much soil each will require (again these are dry soil measures):

4 inch pot (10 cm) = 1 pint (0.5L)

5-6 inch pot (13-15 cm) = 1 quart (1L) = 0.03 cu. ft.

7-8 inch pot (18-20 cm) = 1 gallon (4L) = 0.15 cu. ft.

8.5 inch pot (22 cm) = 2 gallon (7.5L) = 0.3 cu. ft.

10 inch pot (25 cm) = 3 gallon (11L) = 0.46 cu. ft.

12 inch pot (30 cm) = 5 gallon (19L) = 0.77 cu. ft.

14 inch pot (36 cm) = 7 gallon (26L) = 1 cu. ft.

16 inch pot (41 cm) = 10 gallon (38L) = 1.5 cu. ft.

18 inch pot (46 cm) = 15 gallon (57L) = 2.3 cu. ft.

24 inch pot (61 cm) = 25 gallon (95L) = 3.8 cu. ft.

30 inch pot (76 cm) = 30 gallon (114L) = 4.6 cu. ft.

Soil for Hanging Baskets

10 inch (25 cm) = 5.5 dry quarts (6L) = 0.21 cu. ft.

12 inch (30 cm) = 7.9 dry quarts (8.4L) = 0.3 cu. ft.

14 inch (36 cm) = 13.9 dry quarts (15.3L) = 0.5 cu. ft.

Soil for Plant Bowls

8 inch (20 cm) = 1.9 dry quarts (2L) = 0.07 cu. ft.

10 inch (25 cm) = 3.7 dry quarts (4L) = 0.14 cu. ft.

12 inch (30 cm) = 5.5 dry quarts (6L) = 0.21 cu. ft.

14 inch (36 cm) = 8.4 dry quarts (9.2L) = 0.29 cu. ft.

16 inch (41 cm) = 12.0 dry quarts (13.2L) = 0.46 cu. ft.

18 inch (46 cm) = 18.8 dry quarts (20.7L) = 0.73 cu. ft.

21¾ inch (55 cm) = 31.2 dry quarts (34.3L) = 1.21 cu. ft.

Soil for Oval Planters:

12 inch (30 cm) = 3.8 dry quarts (4.1L) =0.14 cu. ft.

16 inch (41 cm) = 7.3 dry quarts (8L) = 0.28 cu. ft.

20 inch (51 cm) = 9.4 dry quarts (10.3L) = 0.36 cu. ft.

Soil for Square Planters:

12 inch (30 cm) = 11.2 dry quarts (12.3L) = 0.48 cu. ft.

15 inch (38 cm) = 23.0 dry quarts (25.3L) = 0.89 cu. ft.

Soil for Window Boxes:

24 inch (61 cm) = 11.7 dry quarts (12.8L) = 0.45 cu. ft.

30 inch (76 cm) = 15.6 dry quarts (17.1L) = 0.6 cu. ft.

36 inch (91 cm) = 19.7 dry quarts (21.6L) = 0.76 cu. ft.

Soil for Strawberry Pots:

5 gallon = 14 dry quarts (15.4L) = 0.54 cu. ft.

Also of interest:

Reader Interactions


Hi this is Maniraj a research scholar from India I would like to know how to calculate volume of a pot and also what does it mean by 1litre of soil.

A litre of soil is the amount of soil that will fill a litre container which is 10cm x 10cm x 10cm.

Volume of a pot… I have a 9 inch diameter pot in front of me as an example… 9 inch top diameter and 7 inch bottom diameter= average diameter of 8 inches.. Formula is.. “Pi” multiplied by “R squared” Radius squared, then multiply that product by the height… So in my case with a nine inch pot I have Pi (3.14159) times (4×4) or 3.14159 X 16= 50.25 square inches multiplied by 8 inches height equals 402 cubic inches. If you want cubic feet then divide the 402 cubic inches by 1,728 cubic inches per cubic foot and you get .237 cubic feet. The 8 1/2 inch container is listed as being .3 cubic feet; the actual measurement would be about .2 cubic feet.

what is the density of potting soil?

Soil density can be measured in a few ways. The presence of sand, silt, loam and organic matter can vary from one soil sample to another–whether you are measuring garden soil or potting soil. Sometimes soil density may include the effect of moisture on the soil. For gardeners, the most common way to measure soil density (garden soil or potting soil) is the hand test: simply grab a handful of soil and squeeze it into a ball. If the soil crumbles apart into many pieces and will not reform when you squeeze it again, then the soil is uncompacted and dry; this soil might be termed light or friable. Soil that breaks apart into a few large chunks that easily reform when you squeeze them is a sign of uncompacted soil with a good amount of moisture. Compacted soils will not break apart in your hand, but are malleable and plastic-like in their consistency when moist; then are hard and unbreakable by hand when dry; this soil would be termed heavy or dense. Other ways to measure soil density include the Protor test; this test requires that three different layers of soil are placed into a cylindrical tube in sequence. A standardized weight is dropped onto the soil repeatedly and the results are measured. The sample then dries overnight and is weighed in order to measure the moisture content. The Nuclear Density Gauge Test is done with a small device that can be transported between testing sights. It operates by measuring the occurrence of a radioactive isotope in the soil in one of two ways. Either by generating small doses of gamma rays that hit the soil surface and then measuring the backscatter–reflection–of the radiation, or by inserting a probe into the soil which transmits the gamma rays directly. Dense, compacted soils absorb more radiation than uncompacted soils. Nuclear density gauges are an expensive, but accurate, timely and effective means of measuring soil compaction.

With 5kgs of potting mix soil, how many medium sized small sized pots can be filled?

Container and growing pots come in a variety of sizes. In the United States nursery and garden centers sell pots by the size in inches and gallons. In the