How do you convert inches to sq inches?

It's not a matter of converting. It's a matter of deciding what you are going to measure. Inches measure length. An ordinary desk ruler is 12 inches in length. A yardstick, three feet, is 36 inches long. Square inches measure an area, not a length. The area of an ordinary standard (8.5 inches by 11 inches) piece of printer paper is calculated by multiplying the two dimensions together: 11 X 8.5 = 93.5 square inches.