There are so many different kind of pots. Some are wider, some are taller. In respect to inches, I cannot see how you could convert gallons to inches, since there is not a standard width/height. Try to think of a gallon milk jug and imagine 2 of those together. Since you posted this in the banana forum, I assume that you are planting a banana? If so, you don't have to follow exactly the pot size as instructed. What kind of plant do you have and how big?

Yeah they do make this confusing, don't they? I have always believed (and a friend who has been in the nursery business confirmed for me) that its a way for the mass market industry to charge more for plants, by container size, not necessarily PLANT SIZE.

The "kind of accepted" standards are these:
a 4" pot= a pint
a 5/6" pot= a quart
an 7/8" pot= a gallon
(there are also 2 gallon sizes, though harder to find)
a 10" pot = a 3 gallon
a 14" pot= a 7 gallon
a 20" pot= a 10 gallon
a 24" pot = a 15 gal
a 30" pot= a 20 gal
a 35" pot = a 25/30 gal

Thanks a lot Bihai! I repotted my 10 inch DC in a 15 inch pot (hopefully be there a while) and it looks great!

If the pot was a perfect cylinder (the bottom was the same size as the top like a bucket) then the formula would be

gallons = pi * (diameter in inches / 2)**2 * height in inches / 1728 (number of cubic inches in a cubic foot) * 7.5 gallons per cubic foot

So for a 6 inch pot by 6 inches high = 0.7 gallons
10 inch by 10 inch high = 1.7 gallons
12 inch by 12 inch high = 5.9 gallons
15 by 15 = 11.5 gallons

For tapered pots take off 20% or so.

Another way to measure is plug the drain hole and start pouring water in a gallon at a time.

Hey!!!
Thanks for the great question and ALL the wonderful info...This could be very good info to have..
Chena

This is the most confusing things I have ever heard.I have a calculator which tells me 16 inches pot equal 8 gallons and 9 inches pot equal 4.5 gallons. This nursery is selling plants which is claiming that it is 2 gallons plant in 4 inches pot. How in the world you can get two gallons in 4 inches.
I relieved my self of all this headache. I plant every thing in 16 inches pots and get my strong sharp drill and drill lots of holes in the pot then plant the pot itself in the garden soil. It is very handy because our winter here freezes every thing so I dig my babies and take them inside the garage to sleep. Now I am wheeling them out of the garage into the yard because it is sunny and over 50, then at night I wheel them back into the garage. I know it is a back breaking work but my babies are happy and started having little green leaves. When I get my hand on teh sweet fruit all the pain in my back will be forgotten.

I found a converter

one qupic inch = .0043 Gallons

X

WOW - this is a really old thread that I didn't even know anyone answered after 2006 but I see two answered in 2011 and now an X (what does this mean?)

BTW - since a cubic foot is equal to 7.5 gallons then a cubic inch is equal to 7.5 gallons / 1728 (cubic inches in a cubic foot) = 0.0043 gallons as foolishpleasure mentioned back in 2011.

And there is no way to put two gallons in a four inch pot unless the pot is 36 inches tall! (assuming a round pot)