Let's see if we can give you a better understanding of feet, square feet, inches and square inches. You can easily change one foot into inches by just multiplyng by 12. You can't convert a square foot into inches, but you can convert it to square inches. Here's how. You have a box of 1" tiles, so each tile is a square of side 1". Picture a square with side 1'. How many 1" tiles will you need to fill it? You need 12 along the top, but you also need 12 down the side, so you need 12 rows of 1" tiles, which is 12 times 12=144. That's how you convert 1 sq ft to sq inches. You multiply by 144. So 3.5 sq ft=3.5*144=432+72=504 sq in. You would need 504 1" tiles to fill a 3.5 ft square.