The chest is regarded as the most significant measurement for making a jacket. It is the width that determines the overall size of the jacket – and it cannot be altered easily, so you had better get it right!
When buying off the rack, the tagged size refers to the measurement of the chest. If the dimension of your chest is 42 inches, you need to wear a size 42 jacket.
It’s important to remember the size refers to the wearer, not the measurement of the suit; many people have a misconception that a jacket of size 42 itself measures of 42 inches around its circumference at its widest point.
In fact most jacket manufacturers and tailors cut the chest of the jacket around four inches larger than the actual size of the wearer’s chest – so a size 42 jacket will actually have a chest measurement of 46 inches.
To measure the chest of the jacket that fits you properly, you need to lay it on a clean surface at first and then button it properly. If the men’s suit jacket has two or three buttons, you need to button the second one only. However, if the jacket is double breasted, you need to button it totally.
Stretch the jacket out to get an accurate measurement. While taking the measurement of the chest of the jacket, start measuring from one arm pit seam across the chest to the opposite arm pit seam.