Figuring how much water in a pipe

Hi all,
A while back there was a discussion about various water tanks and a pvc tank under the floor for a tear, might have been something MadJack had done, not sure. Anyway, I'm thinking about building a passive solar hot water heater to place on the roof of my TTT. But as I was researching solar water heaters, I started to wonder how much pipe would be needed for five gallons of water.
I'm thinking in terms of 3/4" copper pipes. How many feet would I need to get 5 gallons?
I'm also thinking, it might just be a lot easier to purchase one of those camping five gallon bags at Wally World for a few bucks rather than make an actual solar tank.
Anyway, if it isn't too much trouble would one of you, who knows this kind of formul, be able to figure how many feet of pipe I would need to equal five gallons?
Thanks in advance,
Lynn
A while back there was a discussion about various water tanks and a pvc tank under the floor for a tear, might have been something MadJack had done, not sure. Anyway, I'm thinking about building a passive solar hot water heater to place on the roof of my TTT. But as I was researching solar water heaters, I started to wonder how much pipe would be needed for five gallons of water.
I'm thinking in terms of 3/4" copper pipes. How many feet would I need to get 5 gallons?
I'm also thinking, it might just be a lot easier to purchase one of those camping five gallon bags at Wally World for a few bucks rather than make an actual solar tank.
Anyway, if it isn't too much trouble would one of you, who knows this kind of formul, be able to figure how many feet of pipe I would need to equal five gallons?
Thanks in advance,
Lynn