The best evidence is that the average North American woman now wears a US size 9 shoe. But how did we come to this conclusion?
Like us, you may have heard that the average woman’s shoe size is now a US size 9.
Or perhaps you have been told that size 8.5 is the “new size 7”, meaning that 8.5 is the most common women’s shoe size today.
Maybe you have even read that the average female shoe size has increased by one and a half sizes over the last 10 years. And that feet are continuing to grow, meaning today’s average shoe size will be smaller than average tomorrow.
But there is a problem.
There is absolutely no official or study data that actually backs up what the average shoe size for women is.
Every opinion about average shoe size is an educated guess at the right number.
So why do we say that size 9 is the size that is most common amongst American women, whether in heels or flats? The answer is part-data and part-intuition.
Data: the evidence for size 9 being the most popular women’s shoe size
In 2017 and 2018, a total of 1.2 million foot scans were collected from customers who came to bricks and mortar stores to buy shoes in various places around the world. The scans were collected by a 3D scanner on which the customer stood either barefoot or in socks.
Researchers classified the foot measurements into “length classes” starting at 0 mm with 5 mm length intervals (5 mm is approximately 1/5th of an inch). Each foot was classified into the length class that was nearest to the foot length.
The data was then sorted by location, in our case North America being the relevant area.
The authors of the paper concluded that the most frequently occurring length class for female customers was 245 mm for scans in North America: Jurca, A., Žabkar, J. & Džeroski, S. Analysis of 1.2 million foot scans from North America, Europe and Asia. Sci Rep 9, 19155 (2019).
But how does this map to shoe size?
The key is that shoes need to be slightly bigger than the feet that go into them.
Zappos says that a size 8.5 maps to a foot length of 246 mm, and a size 9 to 251mm. So based on allowing a little bit of room at the front, we think that the most frequently occurring female foot size would map to a size 9 shoe.
Of course there are many problems with this conclusion that size 9 is the most popular women’s shoe size. In the end, it can only be approximate.
We’ve used Zappos’ guide since they are a big, widely respected shoe store, but Zappos itself notes that the numbers are only a guide.
Equally significantly, measuring length is only one measure of a foot. The foot is a 3D object and the width and height will also impact shoe size. There were also limitations with the data on foot length which are discussed more fully in the paper.
Finally, shoe size is not entirely objective. We can measure the lengths of women’s feet and get an objective measurement from the ruler. But the trouble with shoe size is that it depends, to an extent, on personal preference.
Basically some women like their shoes to be tighter than others.
Adding to this is that different shoe manufacturers have different lasts for different sizes. In other words, just being a size 9 in one shoe doesn’t mean you’re the same size in every shoe.
Nevertheless, turning to our own intuition (including what women tell us), we do think size 9 is probably the most popular size. It matches with at least one retailer’s shoe size guide and can be logically explained by reference to the data explained above.
We’ve considered some other approaches below.
Was a US size 9 the most popular women’s shoe size in 2002?
Debate has actually raged for decades about the most popular women’s shoe size.
The question of women’s average shoe size was raised in earnest in 2002. Two articles were published within months of each other, both dealing with the topic in detail.
The first was on May 10, 2002, by Jennifer Howard on Slate. It stated that “By now, the average women’s size could hover somewhere in the 9s”.
On September 10, 2002, Mackenzie Carpenter of the Pittsburgh Post-Gazette reached a similar conclusion: “The average woman’s size has risen from 4 1/2 in 1900 to nearly 9 today” she said.
In 2003 the Chicago Tribune also climbed aboard the size 9 bus.
The most popular size in women’s shoes, the Tribune stated, was now “an 8 1/2 and sometimes a 9”.
But what was it all based on?
Each of these articles acknowledged the lack of published data.
Almost all articles on the internet quote a single source to say that “foot size (in both men and women) has grown by a size or so over the past three decades”. That source is an article dated 15 October, 2012 in the Minneapolis Star Tribune.
The article claimed that the National Shoe Retailers Association tracks sizes. The article reported the then Chairman of the organisation saying that “For women, we say 8 1/2 is the new 7”.
This comment is no doubt partly right; shoe sizes have grown and a female American foot is more likely to be an 8 1/2 than a 7 these days as the 2019 study above shows.
But there are some problems with treating this comment as data when it is really only presented as a what some industry people are said to be saying. It’s also over a decade old. So if feet are continuing to grow then it is a little out of date.
The Chairman certainly didn’t say “our members sell more size 8 1/2s than any other size these days, and here are the numbers that prove it.”
In other words, this comment is good evidence to support that size 9 or thereabouts may be the most popular size. But it shouldn’t be taken as literally meaning that 8 1/2 was established by data as the most popular size in 2012.
William Rossi quotes on shoe size increases
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Most internet stories on women’s shoe size also quote the late shoe historian William Rossi as explaining the growth in women’s shoe size to now-defunct lifestyle blog Divine Caroline.
For example, here’s what Time Magazine said in 2012: “People are getting taller and heavier, as they have for generation after generation, Podiatric historian William Rossi told the lifestyle blog Divine Caroline. And their feet are getting larger in proportion to their bodies.”
So why shouldn’t we trust Time Magazine?
Let’s start with the most obvious problem with this apparent conversation: William Rossi passed away in 2003 at the age of 92, four years before the Divine Caroline website launched in February 2007 (you can see the pre-launch splash page and first articles at the Way Back Machine).
So unless Rossi was telling Divine Caroline about women’s feet from beyond the grave, this conversation simply never happened.
Nor does the original article on Divine Caroline suggest that it did.
The Rossi quote is actually way older. The William Rossi quote actually comes from 2002, in an article in the Pitsburgh Post-Gazette (archived here).
Rossi’s point was that the shoe industry hadn’t caught up with the growth in foot sizes. He argued that shoe manufacturers and retailers had no data about what sizes women actually wore as opposed to what they bought.
Rossi’s argument was that the lack of availability of big sizes forced consumers to “cram their feet into the shoes even if they’re not the right size”.
This may have been right, or partially right, over 20 years ago (largely before online shoe sales). But it doesn’t really help us with shoe sizes today.
Some conclusions
It seems almost incredible that there is no more detailed data on average shoe size than the information we have presented above. After all, feet are one of the most studied body parts in history. And shoes – particularly high heels – are the subject of literally hundreds of scientific papers.
Even the government has not entered the field. The National Center for Health Statistics has lots of body measurement data, but has never studied average shoe size for adults (the only time it investigated foot size at all only covered children aged 6 to 11).
Yet based on everything we do know, we can conclude that the average woman’s shoe size in America is currently a size 9 probably. At least until someone comes up with some better data or a reliable argument to the contrary.
Feature image credit: Photo by Alfonso Scarpa on Unsplash