I can't actually give these a star rating, as I was unable to use them - they don't fit at all and I will be returning. It was pretty disappointing as I was really looking forward to adding them to my kit. However, I wanted to post a review to help others people who might have questions about sizing.
I am 5'3" and female, but I power lift and have played a lot of sports over the years so I am very thick/muscular. Reading the reviews, I saw a lot of people commenting that these gaiters are way too small so I ordered the L/XL, thinking that surely they would fit me if they fit 200lb men. To my disappointment, they do not come even close to fitting around my calf. The reason: I AM SHORT. These gaiters are a smaller, lighter pair meant to come just above boot height - on a tall person, they sit a little way above the ankle. On me, they come up to the thickest part of my calf muscle which is much bigger in circumference.
Choosing size based on shoe size is not really helpful - measurements are. So, here you go and hope this helps.
For the L/XL:
~13" across the top/between the snaps, the part that will wrap around your calf
~10.5" in length, measured along the back seam
For fit, I would suggest measuring 10.5" from above your heel/where the bottom of the gaiter would sit, up the back of your leg. Then, see how wide your leg is at that point to decide if these will fit or not.
I wish FL would post this information, I emailed customer service to get measurements but was given different numbers.