How To · Fashion · Build
Why your shoe size isn't the same across brands—and how to size correctly every time
Your size 8 at one brand might be a 9 at another—and that's completely normal. Here's how to decode the inconsistencies and nail your fit.
5 min read · IrisShoe sizing is not standardized. Unlike clothing, where a size 8 dress might fit consistently across brands, footwear manufacturers use proprietary lasts (the wooden forms shoes are built around) that vary wildly. A size 8 at Nike might feel roomy while a size 8 at Adidas pinches your toes. Add in regional differences—European brands often run smaller, Japanese brands tend toward narrow widths—and you're left guessing at checkout.
The good news: sizing inconsistency is predictable once you understand the mechanics. By identifying your true measurements and learning which brands align with your foot shape, you'll stop buying shoes that don't fit and start building a collection that actually works.
Your foot doesn't change. The lasts do.
What you'll need.
- 01Ruler or measuring tape
- 02Paper and pen
- 03Brannock device (or online converter)
- 04Your existing shoes
- 05Brand website and sizing guides
- 06Online size converter tool
Step one · 2 minutes
Measure your feet properly at home
Grab a ruler, a piece of paper, and wear the socks you'll actually wear with shoes. Stand on the paper with your heel against a wall and mark where your longest toe ends. Measure in both inches and centimeters. Do this for both feet—most people have one foot slightly larger. Repeat the measurement in the afternoon when feet are naturally swollen from the day; this gives you a realistic baseline, not an optimistic morning measurement.
Measure on a hard floor, not carpet. Carpet compresses and gives false readings.
Step two · 2 minutes
Identify your Brannock size as a reference point
A Brannock device is the metal foot-measuring tool used in shoe stores—it's the industry standard. If you have access to one at a local shoe retailer, use it. If not, use an online Brannock converter to translate your paper measurement into a Brannock size. This number becomes your anchor. It won't be your size in every brand, but it's the objective starting point for all conversions.
Many specialty running stores offer free Brannock measurements. Call ahead to confirm.
Step three · 2 minutes
Chart your actual size in brands you wear regularly
Pull out shoes you already own that fit well. Write down the brand, the style, and the size marked inside. Do this for at least three pairs across different categories—sneakers, flats, heels, boots. You'll start seeing patterns. You might discover you're consistently a half-size larger in one brand or that a specific brand's width runs narrow. This personal sizing chart is more reliable than any general conversion guide.
Include the shoe's age. Brands sometimes adjust their lasts over time, so a 2019 pair might fit differently than a 2025 version.
Step four · 2 minutes
Understand why brands differ and use that knowledge
European brands (Clarks, Birkenstock, Gianvito Rossi) typically run small; Asian brands (Asics, Onitsuka Tiger) often run narrow; American athletic brands (New Balance, Saucony) tend toward generous widths. Luxury brands frequently use smaller lasts to create a sleeker silhouette. Knowing the brand's origin and positioning helps you predict whether you'll size up or down before you buy. Check the brand's website for their specific sizing notes—many now include comparative charts.
Read customer reviews on retailer sites. Reviewers often note 'runs small' or 'true to size,' which is invaluable real-world data.
Step five · 1 minute
Use conversion tools strategically, not as gospel
Online size converters exist, but treat them as suggestions, not rules. They're based on averages and don't account for your specific foot shape or the particular shoe style you're buying. A ballet flat and a hiking boot in the same brand size fit differently because of how they're constructed. Use converters to narrow your search—if you're a size 8 in Nike and looking at Adidas, start by trying a size 8.5—but always verify with reviews or return policies.
Retailers with free returns (Zappos, Nordstrom, most online shoe sites) let you order multiple sizes and send back what doesn't fit. Use this strategically when trying a new brand.
Step six · 1 minute
Test fit before committing to a full collection
When trying a new brand for the first time, buy a single pair first. Wear them indoors on carpet for a few hours to test comfort without committing. Check for heel slip, toe room, and arch support. If they work, you now have a data point for future purchases from that brand. If they don't, you've learned something valuable without wasting money on multiple pairs.
The 'break-in' myth is real for some shoes but not others. Quality leather stretches slightly; synthetic materials generally don't. Know which you're buying.
How to know it works.
You've nailed your sizing when you can confidently order shoes online without trying them on first, when you stop returning shoes due to fit issues, and when you understand exactly why a shoe from Brand A feels different than Brand B. Your personal sizing chart becomes a reliable reference that saves time and money.
Questions at the mirror.
I measured my feet and got a size that doesn't match what I usually wear. Which is right?
Your measurement is right. Your usual size is based on whichever brand you've been buying, not your actual foot. Use your measurement as your Brannock reference and adjust from there.
Should I size up or down if I'm between sizes?
It depends on the shoe type. For heels and snug styles, size up slightly for comfort. For athletic shoes and boots, go with your exact size or slightly down for a secure fit. Always check the brand's specific guidance.
Why do the same brand's shoes fit differently in different styles?
Different shoe styles use different lasts. A ballet flat, a sneaker, and a boot from the same brand are built on completely different forms, so sizing can vary by a half-size or more within one brand.
Do shoes stretch over time?
Some do, some don't. Genuine leather stretches slightly with wear. Suede stretches a bit. Canvas and synthetic materials rarely stretch. Quality matters—cheap shoes don't improve with wear; good ones often do.