A pipe is a cylinder and the volume of a cylinder is it's radius squared X pie X it's height. 12 inches of 10" pipe would hold more water than 12 inches of 1" pipe. In the same way 12" of 3 inch pipe would hold more water than 1 inch of pipe 3" in diameter. So what you're missing in this equation is; how long is the pipe?
Once you figure out the volume of the pipe, you'll have to convert that amount into gallons. If you're measuring the pipe in inches your end answer will be in cubic inches, you might be hard pressed to find a conversion table for that. Maybe not.
U.S.Gallons of water per foot = volume in cu. in. divided by 231 cu. in.(for U.S.gal)
= (Pi/4 x 32 x 12) / 231 = 0.3672 U.S. gal per foot of 3 inch pipe.
One foot of 3 inch pipe will hold approximately 0.625 gallons of water.
half a pint
This cylinder will hold up to 3,760.11 gallons of water.
141.06 gallons
A 15 cubic foot tank will hold a maximum of about 112.2 gallons of water.
About 14,351 US gallons of water.
700 gallons
You haven't said how deep it is. To measure volume you need three dimensions.
If you filled it all the way to the top it would be holding about 15,594 gallons of water. If you filled it to three feet deep, it decreases to around 10,200 gallons.
A 7 cubic foot freezer can hold approximately 52.44 gallons of water (1 cubic foot is roughly equal to 7.48 gallons).
17,000 gallons
0.212 331 gallons per foot.