To measure the around Bust/Chest Measurement, you need to put the measuring tape 1 inch below the armpit of one to the other as shown in the reference image below.
Sizing Guide - Goal Five
Men's size Guide
How To Take Your Measurements – Bliss Artisanal Lingerie & Accessories
A Fit Guide for Finery's core uniform styles - Finery LA — Elevating the uniform to a craft
Understanding Dress Shirt Measurements
How To Measure Yourself?-Takerlama
Average Chest Size For Men & How to Measure Your Chest – Fitness Volt
Men's Size Chart - How to Measure
Measuring Guide