I ordered the XXL even though it is one size larger than my usual petite XL and I'm very glad I did. I would say that these shirts run slightly smaller than the measurements on the chart.  This is not a boyfriend
big' shirt with a straight cut.  The sides/waist taper slightly and so, a larger size is needed for my waist and hips.  The main reason I like this shirt is because it is 100 percent cotton that is not treated with wrinkle resistant chemicals.  I've been searching for a long time for a cotton shirt just like this and my only gripe is that it is a tiny bit long on my 5'2 frame.  It hangs like a tunic with high sides  hitting at my hip.  The sleeves are a bit long but that's not a huge issue for me.  There are two buttons on the cuff for adjustment and the sleeves can be easily rolled up.  The cotton is super soft and not heavy and I've washed and dried mine on low and it came out without a wrinkle. The seams match and the pocket matches and is undetectable.  I will be able to wear this shirt in hot humid weather.  The shirts are packaged very well.
UPDATE:  I now have the black, lavender and red/white/blue shirts and love them all.  I think the lavender color seems a little bit larger than the others but I don't mind at all.  I don't wear fitted shirts but hate sloppy looking big shirts so these are perfect for me.  There is plenty of room in the chest for me ( I wear a 38-40C) and although it may seem a bit 'relaxed' , it drapes beautifully and doesn't look sloppy and doesn't wrinkle like linen does.  I usually wear this shirt un-tucked with slim pants/jeans and it looks fine but I also wear it tied.