If you are going to get new furniture, you really need to start by measuring the room. This should be done before you make the purchase, rather than after. You do not want to find that the furniture that you purchased will never fit in the room in any configuration. You are much better off to measure twice before you buy it, planning out exactly what you need to make sure that you order the right thing. This saves you a lot of hassle, and it ensures that you do not have to return any of the pieces or swap them out for new ones.
Start by measuring along the wall in a horizontal fashion. Determine where you want the furniture to be positioned. For example, you may want to put the couch directly under the windows in your living room, where it gets good lighting and where it also has a good view of the room. This is a common setup. If the couch is sixty inches long and the windows are 54 inches, you know that you are going to have three inches on either side.
Remember to measure the other items that will go in your room as well. For example, with a 60 inch couch, you need to have more than 60 inches of wall space if you want to have lamps or end tables. You would be surprised by how many people forget about this. They just measure the wall, decide that it will fit, and then find themselves stuck when they cannot get everything into place. If you are willing to sacrifice the lamps and end tables to make the couch work, that is fine, but you should at least know that you are going to be making that sacrifice before you get the furniture into the room.
Next, measure out away from the wall to find out how far the pieces are going to extend into the room. The biggest thing to do is to make sure that you do not block off any doorways that you still want to use. If the couch sticks out halfway across the entry door, it is going to be non-functional and it is going to look bad. It is often easy to visualize how far along the wall a piece of furniture will stretch, but it is harder to think about how much of the room it takes up coming forward, so measuring is very important.
This is also important if you are going to have two pieces that come up to each other in the corner of the room. Remember that you do not want the piece on one wall – a large chair, for example – to go in front of the other piece, like the couch. This looks cluttered, for one thing, and it also makes it so that no one is ever going to sit on the seat with no leg room. This causes you to lose space on both of the walls.