Frustratingly, in the last 2 years, every pair of SmartWool women's socks that I have ordered in my usual SmartWool size (women's small) have been way too small.

I have been a SmartWool customer for 17 years, and have bought many pairs of their "women's small" socks over the years.  A few of the pairs I bought in the past are still unworn (I'm keeping them in new condition while I wear out the pairs in my usual wash-day/seasonal rotations), so I can realistically compare the old "women's small" shape to the new one, between old unworn pairs and new unworn pairs, and the new "women's small" shape is about an inch (or more!) shorter than the old one.

My foot is about a 6 1/2 in the US, a 4 in the UK, and a 37.5 in the EU.  The prior SmartWool "women's small" socks fit my foot really well.  The new "women's small" socks are simply too small in the length and width - they crunch up my toes front-to-back, and pinch them side-to-side as well.

The obvious remedy to the small's being too small would be for me to order a larger size of the same sock model, and I have done so numerous times in the last 2 years -- unfortunately, the women's medium is way too big, leaving a floppy extra inch of fabric beyond my toes.  If I wanted to wear ill-fitting socks with excess material that bunched up uncomfortably in my shoes, I could get them locally and spend less money on inferior brands.

Their current size guide says that their women's small is for up to an EU size 37 and their women's medium is for EU size 38 and up.  I wouldn't think that my foot's falling between those 2 sizes, at 37.5, would translate to the actual, measurable difference of an inch of fabric either way (their current women's smalls are an inch too short for my foot, their current women's mediums are an inch too long) -- it should be more like a couple of millimeters either way.

Unfortunately, I have had to return all the SmartWool socks that I've ordered in the last 2 years, from all manner of retailers.  When I realized it wasn't just a few models or production runs, but apparently a deliberate and permanent re-sizing, I called SmartWool's customer service to complain, and to ask them which of their socks they would recommend would fit me.

They advised that I try their 'everyday' models of wool socks (as opposed to the hiking/running/biking/skiing/performance ones which I had always bought before, using them for things like hiking and skiing, as well as just walking around in athletic/tennis shoes doing general activities and errands, and wearing their socks to sleep in, in the winter), because their everyday models are not made with "technical" fabric and are more stretchy.

I don't really like their everyday socks - I don't like the patterns, I don't like the heights available (I like ankle-height), and I do want my wool socks to be "technical", wick moisture well, stand up to abrasion, and be suitable for hiking/skiing and so forth.

I asked if their men's smalls (in the normal, sports-appropriate sock lines) would fit my foot any better than the new shape of the women's smalls, and they said that the men's shapes had a wider toe box and wider heel.  I don't need a wider heel at all, and normally I don't need a wider toe box when it comes to shoes and socks - my foot is on the narrow side in width, my toes are petite, etc. -- if anything, all the parts of my foot are probably shaped a little smaller than the average American woman's size-6.5 foot.
Even though the heel in the men's small would probably have too much excess fabric for me, I decided to try out a men's small, but then I couldn't find one -- it seems that mainly the smallest size available in their men's lines is medium.

I also considered buying the largest size they make of children's socks (which would be cheaper, too), but the largest children's size is too small for my foot.

It shouldn't be this difficult for them to make a sock that fits my foot size -- my foot is a normal/typical size, here, and in the EU, and in other parts of the world.  It is great that they are making a women's sock that is quite small and better accomodates (I imagine) the women with small feet who wear US sizes 4, 5, and 6, but what about the women who wear from a US 6 to a US 7.5, they also need socks that have a balanced amount of material. They don't want to flop around in technical/athletic socks that are sized for women who wear a US 7.5 to 9.5 (or whatever the size-medium range is).  Smartwool could introduce 4 or 5 (or however many) sizes of sock, they don't have to have the traditional three sizes of small/medium/large.  Make it a marketing feature to provide advanced, tailored sizing... even if the "unusual" or "in-between" sizes might be something that they only sold from their online store, instead of stocking in retail shops.

Over the years, I've tried several other brands of wool socks and I haven't liked any of them as well as SmartWool.  I don't have any other brand to turn to, although I suppose I could try Icebreaker's overpriced sock offerings again.

Athough I don't like SmartWool's merino wool clothing as much as I do other brands' merino wool clothing, I have praised and recommended SmartWool socks on about 50 of my reviews here on Amazon (at the very end of most of my Amazon reviews for merino wool clothing and long underwear).  I feel like I've lost an almost constant companion, because I've probably worn their socks in some capacity on about 80% of the days in the past 17 years.

Thanks to the great deals of about 5 to 15 years ago on Sierratradingpost, I do have quite a few SmartWool pairs that are still serviceable, as well as some still-unworn pairs stashed away, so I'll be okay for wool socks for the next couple of years.
...When you find something that really works well for you, and it's not perishable, buy an extra one as a spare (if it is affordable), because they will probably stop making it sooner rather than later!

In the meantime, I'll have to keep looking around and trying other brands of merino wool socks, which is a hassle, a waste of time and money.

But my size-6.5 loss is probably size 4.5, size-5, and size 5.5's gain, and I suppose that is a good thing for those women, that SmartWool is now making adult women's socks that are not too long and floppy for them.  :-)