The stretch makes these good garments 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 two sizes, I recommend that you choose the largest size you have a measurement in.
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. Measure yourself at the widest point.
Another helpful frame of references is that I am an 8 in Opaline Hue and find that most of my clothes in my closet are a medium or size 8. I recommend ordering what you might generally gravitate towards.
If you have any questions about choosing a size, please contact email@example.com with your measurements.