To determine the square footage of a room, measure the length and width of the room in feet using a tape measure. Make sure to measure at the longest points of the room to ensure accuracy. Once you have these measurements, multiply the length by the width. For example, if the room is 12 feet long and 10 feet wide, the calculation would be 12 x 10 = 120 square feet. If the room has any alcoves or irregular shapes, divide the space into smaller rectangles, calculate the square footage for each, and then add those totals together for the overall square footage of the room.