Be sure your metal tape measure is at least 25 ft. Fifty feet is better. And it’s always a good idea to have a friend help you measure. The measurement will be more accurate when two can hold the tape straight.
Measure the height and width of each wall in the room. Make sure to also measure from one corner to the opposite corner to confirm the room is square or has crooked angles.
Measure all doorways, windows, radiators, fireplaces or any other architectural features.
For windows, measure the height from the floor, along with width and total window height. You will need this measurement if you are placing any furniture against the wall with windows.
Note the location of each electrical outlet.
Note the location of any ceiling light fixtures, railings or any architectural impediments along the way. These can potentially create problems in moving your furniture in if you are not aware of them.