Jon Danniken wrote in news:kja703$d6q$1
@speranza.aioe.org:

On 03/31/2013 09:18 AM, RBM wrote:
I'm trying to figure out how many gallons a tank will hold. I've tried
googling with no help. The tank is 28" x 18" x 16" and it's supposed to
hold 35 gallons. It just seems too small to me. In comparison I have a
tank that measures 13" x 12" x 18" and I'm sure it only holds around 12
gallons. Any help is appreciated.

First, the approximation:

The larger tank is about twice as long, and 1.5 times as wide, as the smaller one, while their
heights are about the same -- so one would expect that its capacity is about 2 x 1.5 = 3 times
that of the smaller tank. If the smaller one is around 12 gallons, you should expect the larger
one to be around 36, which matches well with the claimed size of 35.

Now the exact calculation:

28 x 18 x 16 = 8064 cubic inches. There are 12 x 12 x 12 = 1728 cubic inches in a cubic foot,
so 8064 cubic inches is 8064 / 1728 = 4.67 cubic feet.

One cubic foot is about 7.5 gallons, so 4.67 cubic feet = 35 gallons.

Your smaller tank is 13 x 12 x 18 = 2808 cubic inches = 1.625 cubic feet = 12.2 gallons.