Answer:
Use this formula to calculate water volume:
When you are having your water tested on a regular basis, they will usually ask you what your water volume is. You also need to know this so you can adjust your chemicals as needed. There are some simple formulas to figure out water volume.
For a rectangle, multiply your length (in feet) times the width (in feet) times average depth (in feet) times 7.5.
For a round/oval, multiply your length (in feet) times the width (in feet) times average depth (in feet) times 5.9.
If your pool is freeform, you will be somewhere in the middle. Does your pool resemble a rectangle more, or an oval more? Once you choose a formula, you may have to adjust a bit if your pool has smaller areas or larger curves outside the length and width that you used.
Of course the way to know the exact volume of water your pool takes is to have it filled with a water truck which can only fit so many gallons onto their truck, or if you have metered water, fill the pool and you'll see what you have been charged for.