The measurement is obtained by laying the t-shirt (hoodie, shirt or other top) flat on a flat surface.
MEASURE to find the right coat size — Hamilton County Kids Coats
Size guide for babies and children clothes
Body measurements A: NECK- measure at base of neck. B: CHEST
Chest measurement - Women
How to Measure Your Body for Women's Jackets
Size Guide Get It On Clothing
Tips on Sizing
Fitting Guide - Contare
Applied Sciences, Free Full-Text
What if I don't know what jersey size I am? : GCC OZ