All apparels are measured laying flat.
Measurements are listed in CM and Inches.

To ensure that you have the correct sizing, measure similar items from your closet and compare them with the given measurements.

from armpit to armpit ( x 2 for total front and back )

approx. 5”or 13cm from bust ( x 2 for total front and back )

approx. 7”or 18cm from waist ( x 2 for total front and back)

Top/ Dress: from shoulder to hem
Bottom: from waist to hem

measured across the back from shoulder seam to shoulder seam.

from shoulder seam to the wrist hem

measured wrist hem ( x2 for total front and back )

"Measurement can be confusing sometimes if you prefer images over text, here I've created a list of 4 categories to give you a clear picture of how it works."
"Size does matter." - wabisabi

A gentle reminder before your purchase, kindly look through the sizing chart and make sure you are getting the right fit. 
*General guideline on the estimated modern size, reference from the US
women size chart
"Beauty comes in all sizes, not just size 5." - Roseanne Barr