The stretch makes this a good sweater to fit the varieties among our bodies. The sleeves and chest are true to fit, while the body of the sweater falls a bit more loosely. If you find that you fall in the middle of a size, I recommend that you err on the side of smaller as the sweater is meant to have a slight natural flow.
The best way to take your measurement is to use a measuring tape and find the size that best meets the averages of these measurements. When measuring bust, measure wearing a bra you would wear with this garment.
Another helpful frame of references is that I am a medium in Opaline Hue and find that most of my clothes in my closet are a medium. I recommend ordering what you might generally gravitate towards.
Being a brand new company, we are limited in our resources to offer a greater range of sizing. Smaller and larger sizes will become available as we grow! If you have any questions about choosing a size, please contact firstname.lastname@example.org with your measurements.