I’m a UK size 10 and originally bought a 3 pack of Large/XL, I reviewed the pink sock giving it 5 stars, and stand by everything in that review. However as I have a tendency to pull my socks tight as I put them on and then readjust them, I decided to try the next size down, to compare the fit, and have to say I’m glad I did.
The smaller size feels like it hugs my feet without being too tight ( I did speak with one of the team before embarking on this, with a very quick response, I might add). I tried them out with a 5k run at a moderate pace including some hills and had no issues with comfort or tightness. And so I’ve ordered another couple of packs of 3 pairs in the smaller size, as I feel these suit me better, worth bearing in mind when choosing sizes