You’re standing in a shop in Paris. Or maybe you're scrolling through a Japanese resale site looking for those specific vintage Nikes. You find the pair. They're perfect. Then you look at the tongue of the shoe and see a "42." Or maybe a "9." If you’re from the States, a 9 is a solid medium. If you're in the UK, that same 9 is actually a massive 10 in US terms. It’s a mess. Honestly, the international shoe size chart isn't really one chart at all; it’s a fragmented map of regional traditions, historical leftover math, and brand-specific whims that make buying footwear feel like a high-stakes gambling session.
Feet are weird. They aren't flat, two-dimensional shapes. They’re complex structures with arches, widths, and volumes that change throughout the day. Yet, we try to boil all that biological complexity down to a single digit. It’s a bit ridiculous when you think about it.
The Three Kings of Sizing: US, UK, and EU
Most people deal with these three systems. But they aren't even based on the same units of measurement.
The UK system is the oldest. It’s based on the "barleycorn." Yes, an actual grain of barley. Back in 1324, King Edward II decreed that three grains of barley laid end-to-end equaled one inch. In the world of UK shoemaking, a size zero was fixed at four inches, and every full size added since then is exactly one barleycorn ($1/3$ of an inch).
The US system tried to be different but stayed pretty close to its British roots. A US men’s size is generally one full size larger than a UK size. So, a UK 8 is a US 9. Except when it isn't. Women's sizing in the US is a totally different beast, usually sitting about 1.5 to 2 sizes above the UK equivalent. If you're a woman wearing a US 8, you're looking for a UK 6 or 6.5. It’s enough to give anyone a headache.
Then there’s the European (EU) system. They use the "Paris Point." One Paris Point is $2/3$ of a centimeter (about 6.67 millimeters). This system is actually more precise because the increments are smaller than the chunky barleycorn steps of the US and UK. It’s why you’ll often find that a European 42 feels "just right" while a US 9 is too tight and a 10 is too loose. There’s more granularity there.
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Why Your "True Size" is Probably a Lie
Have you ever noticed how you’re an 11 in Vans but a 10 in Clarks? Or maybe a 12 in running shoes?
Brand "last" is the culprit. A last is the plastic or wooden mold that a shoe is built around. Brands like Nike and Adidas use proprietary lasts based on their own target demographics. Running shoes are almost always sized smaller because the manufacturers assume you want a snug fit for performance, or they account for the fact that feet swell during a five-mile run.
Brannock devices—those cold, metal sliding contraptions in shoe stores—are the gold standard for measurement, but even they have limits. They measure length and width, but they don't measure "girth" or "volume." If you have a high instep, an international shoe size chart becomes a mere suggestion. You might need to size up two full units just to get your foot into the opening of a Chelsea boot, even if the length is technically correct.
The Mondopoint Revolution (That Hasn't Quite Happened)
There is a hero in this story, though it’s a quiet one: Mondopoint.
Invented in the 1970s and standardized by ISO 9407, Mondopoint is the most logical system on Earth. It measures the foot in millimeters. Length and width. Simple. If your foot is 280mm long and 110mm wide, your size is 280/110. No barleycorns. No Paris Points. No confusing gender offsets.
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You see Mondopoint most often in ski boots and military gear. Why hasn't it taken over the world? Because fashion is stubborn. Transitioning every factory in Vietnam and China to a new numbering system would cost billions. Plus, brands like the "prestige" of their specific fit. If you know you're a "Size 40" in a luxury Italian brand, that's part of the brand's identity. Switching to "255mm" feels a bit... clinical.
Global Variations You Need to Know
Let’s talk about Japan. Japanese sizing is essentially a simplified Mondopoint. It’s measured in centimeters. If you see a 25 or 26, that’s the length of the foot the shoe is designed for. It’s incredibly easy to use. If you know your foot is 27cm long, you buy a 27. Done.
China uses its own "New Size" system which is also centimeter-based, but you'll often still see older European numbering in street markets. Brazil is the real curveball. Brazilian sizes are usually two numbers lower than European sizes. So, a European 39 is a Brazilian 37. If you’re ordering flip-flops from a Brazilian brand online, double-check that conversion or you’ll end up with something fit for a doll.
The Width Factor: The Forgotten Dimension
Most international charts ignore width entirely. In the US, we use letters: B (narrow), D (standard), E, EE, and EEEE (extra wide).
In the UK, they use a different alphabet. F is usually standard, G is wide, and H is extra wide. If you’re looking at an international shoe size chart and it doesn't mention width, it's almost certainly a "standard" (D/F) fit. For people with wide feet, this is the primary cause of shoe-buying heartbreak. You can find the perfect length in a European 44, but if it’s a sleek Italian last, your wide foot is going to feel like it’s in a vise.
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How to Actually Measure Your Foot at Home
Stop guessing.
Tape a piece of paper to a hard floor (not carpet). Stand on it with your full weight. Have someone else trace your foot with a pen held perfectly vertical. If you do it yourself, you’ll lean over and change the shape of your foot, ruining the measurement. Measure the distance from the back of the heel to the tip of your longest toe (which isn't always the big toe!).
Do this for both feet. Most people have one foot that’s slightly larger. Always buy for the larger foot.
Take that measurement in millimeters. Now, when you look at an international shoe size chart, ignore the US or UK columns first. Look for the "CM" or "MM" column. That is your anchor. Use that number to find the corresponding regional size. If you're 273mm, you're looking for a size that lists a 27.5cm internal length.
Actionable Steps for Your Next Purchase
Buying shoes shouldn't be a gamble. Here is how to handle the chaos of international sizing:
- Trust the Centimeters: Always look for the CM or MM length on the size tag. It is the only universal constant across brands.
- Account for Socks: If you’re buying winter boots, measure your foot while wearing the thick wool socks you plan to use. It can add half a size of volume.
- Check the "Last" Reputation: Before buying, Google "Does [Brand Name] run large or small?" Community forums like Reddit's r/goodyearwelt or dedicated running forums are goldmines for knowing if a specific model deviates from the standard chart.
- Afternoon Measuring: Your feet are at their largest in the late afternoon after you've been walking around. Never measure your feet first thing in the morning.
- The Rule of Thumb: You should generally have about a thumb's width of space between your longest toe and the end of the shoe. If your toes are touching the front, the size is wrong, regardless of what the chart says.
The reality is that as long as we use 700-year-old British math and 19th-century French points, the international shoe size chart will remain a bit of a disaster. But if you stick to your measurements in millimeters and understand that every brand is its own little kingdom, you'll rarely end up with blisters.