The Neck to Waist Length is to the back of the body what the Nape to Waist Length is to the front: the basic measurement of the back of the body. If you’re hoping to make a fitted garment work in back, the Neck to Waist and Neck to Shoulder Lengths are what you need.
The Neck to Waist Length measurement is taken down the center back line of the body (generally the spine), from the most prominent bone at the base of the neck (C7) down to the waist. The measurement is taken directly against the body, and the tape should not stray away from the body surface at any point. (The back of the torso is much simpler than the front, isn’t it?)
You will need assistance taking this measurement. To locate the prominent bone of the neck (it doesn’t visibly stick out for a lot of people), lower you head so you’re looking at the floor. Run you fingers along the bones in your neck – towards the base you should find one that seems particularly present. Keep your finger there on your neck, and lift your head. Check in a mirror: your finger should be located above the level of the base of the neck at the front of the body (usually 2-3 inches), and slightly below the level of the muscles of the shoulder. While the measurement is being taken, you should stand normally, with your weight evenly distributed on both feet. This is no time to slouch, nor to suddenly show the world how absolutely straight you can make your spine if you really focus on it. Stand normally. Starting with the tape at the prominent neck bone, measure downwards to the waist line.
As the Neck to Waist Length measurement is being taken, the person with the tape should be looking for the widest area of the back. Traditionally, this is considered the center of the shoulder, but in several figure types it’s located at the level of the armpit or slightly below. Looking at the tape, note how far down the figure the widest area occurs: this is the Neck to Shoulder measure. (We’ll use it for fitting darts and shaping seems later. If you have troubles with jackets binding across the back at the armpit level, or you notice that jackets often ride up and form a big tuck across your shoulders, this is probably where you need special fitting.)
If you have scoliosis or a similar curvature of the spine, take these measurements straight along the center of the figure even if that means the tape doesn’t follow your spine correctly. If you have a prominent sway to your lower back, you might see that the tape pulls slightly away from the body on it’s way to your waist. This is fine. If you have a pronounced hump to your upper back, take the measurement along the center body line over the curve. In this case, you may see that the back length of the figure (Neck to Waist Length) is significantly longer than the front length of the figure (Nape to Waist Length). That’s ok.