Clothing sizes can differ from one brand to another, although their sizing guides typically follow the same sets of measurements.
Measurement charts are used to define all the points of measure (POM) required for the garment specifications.
Sizing guides can vary depending on the manufacturer, and each designer typically provides their own sizing charts. The size chart is a generic estimate of sizes (such as XS through XL.). Each garment can vary from these measurements based on how it’s designed to fit.
Sizing charts are generic and individual brands typically provide their own charts, which might differ considerably from generic sizing charts.
Letter sizing (XS, S, M, L, and XL etc.) tries to simplify the process, but basically every brand has its own definition of those letters.
How to order the right size:
Refer to the garment’s actual measurements. Size descriptions are much more accurate than letter sizing.
If you have clothes that fit you well, measure those and use them as a baseline for shopping online.