While the above chart is the industry "standard" for men's regular body size, the Signature Field Shirts have a good amount of "body ease" built into it. If you are between sizes, order the smaller of the two sizes. Bush poplin is pre-shrunk, so don't expect shrinkage. Machine wash cold is to preserve the color of the poplin.
Each product page provides a chart for the actual spec measurements of the garment on that page.