Just a disclaimer to anyone looking to purchase this armor... I would size your armor based upon your quad... not your calf. I recently purchased the elbow and knee protectors and the knee protector seems to run a little smaller than stated. It will flex/stretch a little but it makes it pretty tough to pedal when you have no blood flowing past your quad =)
Luckily Huck's got an awesome return policy and I'm swapping out for the large. Through reading reviews on other sites, POC seems notorious for running on the small side (unusual considering they only seem to carry small-medium-large). But on the upside, my elbow armor from them is awesome. Even though POC armor is a bit more $$$ buy with confidence knowing you gain better comfort through greater flexibility and range of motion.