Sizing
The best way to get an accurate measurement is to pick one or more of your favorite shirts, lay them on a flat surface, and measure the dimensions as seen in the charts below.
Solid color shirts are true to measurements but semi-fitted; some would suggest going up one size if you prefer a looser look/fit.
Tie-dye shirts are also semi-fitted, but due to the tie-dye process have the potential to run very slightly smaller.