Why shoe sizes stopped being comparable around 2005
For most of the 20th century, a "US Men's 10" was a US Men's 10. The Brannock device — the metal foot-measurer every shoe store used — set a physical length for each size number, and while individual shoes varied in comfort, the length number was stable. Then two things happened. Performance footwear design got serious about foot-shape ergonomics, and every brand started designing its own proprietary last (the foot-shaped form the shoe is built around) to differentiate its products. By the mid-2000s, a "Nike 10" and a "New Balance 10" and a "Vans 10" were no longer the same shoe length, and the gap has only widened.
Today, a serious sneaker or running shoe buyer expects to size up half a size in Nike, true-to-size in New Balance, size down half in Converse, and buy a completely different number in Birkenstock (which is sized in EU only). If you walk into a store, try-on handles this. For online purchases — the majority of non-chain shoe sales since 2020 — the brand-specific offset is one of the single biggest drivers of returns and re-buys. This calculator bakes the offsets into the output so you can order with more confidence.
The three coordinate systems you'll see on a box
US (and the near-identical UK system with a one-size offset) is based on 1/3-inch increments. A half size is 1/6 inch or about 4.2 mm. US Men's and Women's are offset by 1.5 sizes because they were standardized with different reference lengths. UK is usually one full size below US Men's (UK 9 = US Men 10).
EU (Paris Point) uses 2/3-cm increments. A half size doesn't exist in strict EU sizing — Paris Point is a whole-size-only scale — but most brands print half sizes anyway (EU 43.5) to approximate the finer US/UK gradations. A US Men 10 is roughly EU 44.
JP / Mondopoint is the clearest: size = foot length in centimeters, with half-size increments of 0.5 cm. JP 27 = foot 27.0 cm. JP 27.5 = foot 27.5 cm. No offsets, no regions. This is the industry standard used in European military procurement and in Japanese sports footwear, and it's slowly gaining traction in global e-commerce. When in doubt, know your foot length in cm.
Brand-by-brand fit: what 30 years of reviews tell us
Nike runs small, consistently. The Jordan line, Air Max, and most basketball silhouettes fit about half a size tight — a true US Men 10 foot is most comfortable in a Nike US 10.5. The toe box is also narrower than average. Runners with wide forefeet routinely size up a full size in Nike to avoid big-toe impact.
Adidas is closer to true-to-size, with two exceptions. Ultraboost and other Boost-cushioned models often fit about a quarter size large because the foam compresses under the forefoot. Heritage models (Stan Smith, Samba, Gazelle) are accurate. Adidas also sizes more generously in the heel than Nike, which helps narrow heels.
New Balance is the gold standard for US sizing fidelity. A New Balance US Men 10 fits a true-Brannock-10 foot with standard shoe wiggle room. More importantly, New Balance is one of the few major brands that actually stocks 2E (wide) and 4E (extra-wide) variants across most models. For wide-footed runners, New Balance is nearly unbeatable.
Vans runs small and narrow. The Old Skool and Authentic silhouettes are particularly tight in the forefoot. Size up half, and expect another quarter-size of stretch from the canvas over the first two weeks of wear. Vans fit athletic shoes exactly like its heritage shoes in this regard — the last is consistent across the line.
Converse runs large, which is the opposite of what most American shoppers expect given the Chuck Taylor is the canonical "basic sneaker." A Converse US 10 fits a foot that would wear Nike US 11 or New Balance US 10.5. Size down half a size at minimum; some foot shapes need a full size down. The flat, firm insole and very thin arch support also mean Converse is a poor choice for all-day walking — they're a style shoe, not a comfort shoe.
Birkenstock is sized in EU only, and the EU sizing follows the German convention (slightly larger than French/Italian EU). The "regular" width is extremely wide — Birkenstock's whole design philosophy is a roomy cork footbed that molds to your foot over 2-4 weeks of break-in. If you have narrow feet, order the "narrow" width; if you have standard feet, order regular. A US Men 10 is Birkenstock 43 in regular width. The brand does not publish width in mm, so the best proxy is whether you've ever been able to wear wide shoes without feeling like your foot was swimming.
How the calculator converts one brand's size to another
Every brand has a documented or consensus-measured "fit offset" versus the Brannock standard. Nike is +0.5 (runs small), Vans is +0.5, Converse is -1.0 (runs large), Adidas is -0.25, New Balance is 0, Birkenstock is 0 (in its own EU system). The matcher:
- Takes your stated size and subtracts your starting brand's offset. This gives your "true" US Men's size — roughly your Brannock-device reading.
- Converts that true size to foot length in cm (1/3 inch per half size, anchored at US 6 = 22.9 cm).
- For each target brand, adds that brand's offset back to compute the label you should actually order.
- Translates the per-brand US Men's label into US Women's, UK, EU, and JP using the standard regional offsets.
When to trust the number and when to measure
For athletic brands with consistent fit (Nike, Adidas, New Balance, Hoka, Asics, Saucony), the matcher gets within a quarter size the vast majority of the time. For heritage brands with more model-to- model variation (Vans' Sk8-Hi vs Old Skool, Converse's Chuck 70 vs Chuck All Star), there's maybe a quarter-size of residual noise per model. For boots and dress shoes — which are built on proprietary lasts with wildly different heel-to-ball ratios — the matcher is a starting point, not a final answer. For those, the honest advice is to measure your foot in cm and check the brand's own Mondopoint chart.
The single best thing a serious shoe shopper can do is learn their foot length in centimeters, their forefoot width in millimeters, and which last shapes they prefer (pointed vs rounded vs square toe). Once you know those three numbers, shoe shopping becomes measurement rather than guesswork — you can look at any brand's size chart and know within a quarter size what to order.
Kids' sizing is its own mess
If you're shopping for children, none of the above fully applies. Youth sizes (US 1Y-7Y) overlap with adult small sizes but are built on narrower, higher-volume lasts. A child growing into an adult foot often needs a full-size step at the transition point because youth lasts are shaped for developing arches and proportionally wider forefeet. EU sizes are mercifully consistent across youth and adult (a foot of 24 cm is EU 38, full stop), which is one reason European parents have an easier time with online shoe purchases than American parents.
Related tools
- Clothing size converter — US, UK, EU, and JP for tops and bottoms.
- Length converter — for when the size chart asks for cm or inches.
- Weight converter — if you're also sorting through luggage weight limits.
- Travel cheat sheet — country-specific retail sizing quirks.
- Currency planner — if you're buying from an overseas brand.
A final note on returns
Online shoe returns cost the retailer $15-25 and cost the planet real carbon — every box shipped both ways is roughly a kilogram of CO2. The calculator above exists partly to reduce that. If it gets you within half a size of the right answer on the first try, it has done its job. If you're between sizes, the universal heuristic from experienced shoe fitters: size up for athletic shoes, size down for dress shoes, size up for leather (it breaks in to fit), stay true for canvas or synthetic (they don't stretch much). And measure your feet every 3-5 years — adult feet spread and lengthen with age, pregnancy, and weight change.