How many gallons of water to fill a 16 foot round pool?
Cannot be answered with only these measurements. You need to specify what shape the pool is. Also, for a rectangular pool, the length, width and depth are needed. For a round pool, the diameter and depth are needed.
How many gallons in a 33ft round swimming pool?
It depends on how deep you fill the pool. So, let's take the most common depths for a 33-foot round pool; 3, 4 and 5 feet: For 3 feet of water the total gallons will be about 19,275. For 4 feet of water the total gallons will be about 25,700. For 5 feet of water the total gallons will be about 32,125.