I saw this done some time ago on the t.v show 'What not to wear' and decided to give it a whirl myself. What you do is draw a rough sketch of what you think your body shape is against the wall, height/width and all- you could put a large sheet of paper on the wall so not to mark it (we just moved to a a new place and are about to paint anyway) or do it on the garage drywall. Then stand against the wall (in your drawing).......you have someone else trace around your body shape with a pencil (stay very still) then step away from the wall and see what size you really are.
I drew myself MUCH larger compared to the actual trace of my body. It's amazing how we see ourselves. My boyfriend drew himself exactly right......maybe it's a female thing
Just don't let your young kids see you sketching on the walls or there will be lot's of "But, Mummy was doing it!"