There is no sensible answer to this question. A gallon is a measure of volume and and that cannot be converted to a measure of area.
18 x 18 = 324 square feet
18 square meters is the same as 193.75 square feet.
There are: 8 times 18 = 144 square feet
18 square feet = 1.67 square meters.
18 square feet is about 1.7 (1.67225) square meters.
18 US gallons equates to 2.4 (2.40625) cubic feet.
2.25 square feet.
There are 144 18 square inch tiles in an area of 18 square feet.
There are: 18*15.5 = 279 square feet
36in x 18in x 18in = 11664 cubic inches 11664/231 = 50.49gallons
A cylinder that is 18 feet long and has an inside diameter of 4 feet has a volume of about 1,692 US gallons of water.
18 x 12 = 216 square feet.