how do you do square feet
Do the math. You probably know how to calculate the square footage of a simple room without any funny shapes. Just break out your measuring tapeâor a laser measureâto get its length and width. Multiply the width by the length and voila! You have the square footage. Say a room is 20 feet wide by 13 feet long, then 20 x 13 = 260 square feet. How to calculate square feet.