Free Tools - Measurements
A pattern is geometry. It is a series of measurements mapping the body.
It isn´t personal. Clothes, and how they fit is subjective. Some people like a tight fit, whilst others prefer a relaxed silhouette.
If you are uncertain about which size you should choose - because it is stretch, or because it is an outer layer, measure a garment you have that is of a similar fabric or cut and use it´s measurements a guide.
This method is a useful guide in deciding how you may need to alter a pattern to suit your purpose.
Download the measurement guide here. It includes a template that you can use to write down your measurements for future projects.