The girth (chest) measurement is usually best for proper fit and then length. The girth measurement should be taken around the chest, just behind the front legs. The length should be from the nape of the neck (where neck meets the shoulders) to the back legs or tail.
I usually like Ruby's dresses to fit just to her tail, although not covering her tail. So length can be more variable than chest measurement.
Use a measuring tape or if not that a ribbon, string, etc will work and a ruler or yard stick. Use the ribbon around your dog as the tape measure and then get your actual measurement by laying the ribbon against the ruler or yard stick.
Hope this helps and is what you wanted to know..
__________________  ~Ruby, Reno, Razz, & Jack~ |