my guess is 2.75 million gallons roughly. if my math is off forgive me. but the tank itself holds 11,000 tons of water, and figure 5 gallons of saltwater weighs approx. 40lbs. tells me there is 22,000,000 lbs of water divided by 8lbs. tells me 2.75 million gallons. I may be off, I just got home from camping last night and I am a little hungover and tired..