A brief (and surprisingly weird) history of sizing
Shoe sizing has been around since the 1300s. In medieval England, they used actual grains of barley – yes, barleycorns – to measure shoes. One barleycorn equals roughly 1/3 inch. Across Europe, systems popped up independently: “Paris points” in France, “Mondopoint” in Germany, you name it.
The modern EU sizing system comes from France. One size equals two-thirds of a centimeter, measured along the last, a 3D mold that shoes are built around. But here's the catch: that last isn’t your foot. It’s just a model of one. That’s where things get complicated.
What’s a last, and why should you care?
A last is the foundation of every shoe. It’s a three-dimensional model that defines the shape: length, width, arch height, toe curve, heel angle – all of it.
Each brand designs its own lasts to match their look and feel. One might be sleek and narrow. Another might build in extra room at the toe. So two shoes marked as the same size can fit totally differently, simply because they’re based on different lasts.
And yes, EU sizing is based on the length of the last, not your actual foot. That’s one reason a “41” can feel great in one pair and tight in another.
Why length alone isn’t enough
Even if you know your EU size, fit can vary based on:
- Last shape: Some are roomier, others narrow or high over the instep.
- Insole design: Removable or plush insoles can completely change the feel.
- Materials: Leather stretches. Canvas doesn’t. Tech fabrics might hug tighter.
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Country of origin: A size 41 made in Italy? Usually narrower than one made in the US.
"And here’s something most people don’t realize: even major brands like Nike or Adidas often produce the same model in different factories around the world. That can lead to subtle, but noticeable differences in fit, even if the label says it’s the same size.
At Mercer, consistency matters. Each model is made in a single dedicated factory, ensuring a reliable fit across the board. For a few select styles, we work with a second trusted manufacturer, but even then, that model only comes from one place."
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Padding and curve: Extra cushioning, a stiff heel, a curved toe box – it all adds up.
So yes, you might wear a 40 in one brand and a 41.5 in another. Fit is three-dimensional. Measuring length alone isn’t enough.
Width Matters Too: Understanding “D” Width
While most people focus on length, width quietly determines true comfort. In footwear, widths are often marked with letters: B for narrow, D for standard, and E for wide.
At The Mercer Brand, our sneakers are crafted using a “D” width last, the industry’s standard fit for men’s footwear, and a slightly roomier, more universal option for women.
Why “D”? Because it strikes the balance between a refined silhouette and all-day wearability. The “D” width gives enough space across the forefoot and instep to move naturally, without feeling loose or bulky, ideal for that effortless Mercer comfort.
Combined with our meticulously shaped lasts and premium materials, this ensures a consistent fit across every style, from Re-Run to Re-Tennis.
Fun fact: most people have two different feet
Around 60% of people have mismatched feet – often, the left one is slightly bigger.
- A difference of up to half a size is totally normal.
- But most stores measure just one foot – usually the right.
Tip: Always measure both feet and size to the larger one.
Mercer’s guide to getting it right (especially online)
We want your sneakers to feel just right; no pressure points, no guesswork. Here’s how to dial it in:
1. Start with what you know
Measure both feet, and check your size based on your "last" length. Do it standing, later in the day. Trace heel to toe, and use the bigger foot. Add 0.5–1 cm for movement and sock room, which totals roughly the same length as your "last".
*CM stands for the length of the last — the 3D mold your sneaker is built around — measured in centimeters.
2. Read our fit notes
We test every model ourselves. If the fit runs snug, roomy, or narrow, we’ll call it out. We mention it right on the product page, no guesswork needed.
3. Still unsure? Ask us
Shoot us a DM, start a chat, or send us an email — we’ll help you compare based on what you already wear. Also, ask yourself: do I know my size in a brand, or my actual last size? That’s the best starting point.
4. Socks make a difference
Thick socks in a snug shoe can feel tight. Thin socks in a roomy one might make you slide around. Choose accordingly.
5. And always remember: the last is everything
It shapes how the shoe actually feels. Sizing is just a starting point.
Bottom line: comfort isn’t a number
Your best fit is about feel, not just a shoe size. At Mercer, we design our sneakers to move with you; from that first step in Re-Tennis to your longest days in Re-Run. Now you’re all set to shop your first (or newest) pair of Mercer sneakers.
