Sorry...dumb question

[Hondanation09]

I am taking delivery of 29 gallon tank tomorrow and getting water ready. I also have 17 pounds live rock and 13 pounds key largo rock. Approximately how much saltwater should I need factoring in Rock and 15 pounds of sand? 20 gallons sound about right?

 

[Audiew]

I think it will be between 20-24 gallons