Shirt Measurements are done as follows:
Bust - Across bust from armpit to armpit
Shoulders - From Shoulder seam to Shoulder seam
Length - From point where Shoulder seam meets the Collar to the bottom hem
Bottom width - Measured across bottom hem
Sleeve Length - From Shoulder seam down to end of sleeve
Armpit to Hem - Measured from armpit to the bottom hem. On shirts with tails this is measured to top of the arch.