It's a little over 13' long on both sides (fence and patio). The shallow end is 34" deep, and the deep end is around 40" deep. Estimated volume for a 13' x13' square with an average depth of 3' is right at 3950 gallons. Mine is roughly a triangle (half a square), so that puts it at 1975 gallons. Now, my pond's average depth is a little over 3', and it's length and width are slightly longer than 13'. I also pick-up some volume because the third side of my triangle is curved outward (not straight), but then I lose a bit because of the raised section in the middle. That's why I say that it's hard to know exactly without using a meter on the hose during the initial fill-up.
I do know that the raised section is a 6' circle that has a water depth of 18". That puts it just over 300 gallons.