When flat, armpit to armpit measures 24 inches. 

When flat, shoulder seam to the bottom of the arm-sleeve measures 25.5 inches. 

When flat, shoulder seam to shoulder seam measures 18.5 inches. 

The measurement from the back/middle collar seam to the bottom of the shirt is 29.5 inches.  

This shirt is in great condition and comes from a smoke-free home.  Thanks for looking!