Area is calculated by multiplying the length by the width. So, if your room is 11 feet wide by 15 feet long, it has a total size of 165 square feet. To figure out the square footage of a room that you already know the dimensions of, use this formula: Area = Length x Width. The area of a room is useful for calculating different amounts related to room size. For example, the cost of building materials is usually based on square feet. The amount of furniture you want for your room is also based on its area. If you want a room with a small area, you can get away with having just one bed instead of two or more beds crammed in there. A large area means you can't stuff as many people into it. You should measure the length and width of a room first before calculating its area. You need to make sure that you include all of the space inside the walls, which means that you can't rely only on what's written on the doorways between rooms. For example, if you leave a room when someone is entering another one, then you've created a bottleneck that reduces the room's overall size. This happens very often when people walk through open doors into empty spaces where they're not expected next.