Fit
A practical way to read garment measurements without confusing them with body measurements.
Check whether the product chart describes body measurements or finished garment measurements. A width measured across a shirt laid flat is not the same as a chest circumference. Use the method and units named on that product's chart.
Choose a similar garment you already find comfortable. Lay it flat without stretching it, then compare the same measurement named in the product chart. Write down both the measurement and its method so you can compare like with like.
Read fit and stretch notes alongside the chart. A close-fitting layer and a roomy overshirt serve different purposes. If the supplied information leaves an important measurement unclear, ask support before choosing a size.