I started out with 16 gallons. I now have about 8.5. It takes 3/4 gallon to do a coat, so I've done about 10 coats. Permadri had recommended 15 gallons for the project. Apparently that calculation is based on 20 sq. ft. per gallon for 300 sq. ft.. The range is 20-30 sq. ft. per gallon. I think my actual sq. ft. is about 288 not 300, so I have some play factor.
I'm not going to open the other 5 gallon container. I'll save that for my 4'x4' tanks. 60 mil is the thickness of two credit cards. I'm pretty sure I have that already and if not should when I'm finished with the rest of the open containers (3.5 gallons).