It is 650 gallons. Together with the upper pond and Bio Reservoir, the total is about 1350 to 1400 gallons.
It was not as much as I wanted, but the design had to be managed based on the area and the 15 foot width of the Home Depot EPDM liner. I have the waterfall with the Bio filter (top left) and the Coral tree (upper left) that could not be moved, and the paver sidewalk with the electrical running underneath to the right. I'm thinking about climbing my tower to get an ovehead (birdseye) picture but not today.
The strategy here was to make a deep pond for the adult breeder stock and use the upper pond for the yearlings (7-9" Koi). I have over a 1000 in tanks right now in 4 different sizes. It is amazing how differently they grow. One is 5 times bigger than some of the smaller ones.