Draw a rectangle where the width is half your bust measurement (plus 2 inches for "ease") and the length is your back length.
Drop the outer shoulder point by about 1.5 inches to mimic the natural slope of the body. BahSeexy_B_n_zip
Finish the neckline with a facing or bias tape for a clean, professional look. Draw a rectangle where the width is half
Measure down from the shoulder for your armscye depth and draw a "J" curve. connect them with a smooth curve.
Add a 1-inch (2.5 cm) seam allowance specifically at the center back. This provides enough "meat" for the zipper teeth to sit securely.
Mark the neck width and depth; connect them with a smooth curve.