How These Size Charts Are Built
This site makes specific numerical claims about 35 brands, so here is exactly where the numbers come from, what is verified, and what is not.
Everything is keyed to foot length
Sizes are never converted from one size number to another. Each brand's chart is stored against measured foot length in centimetres, and a lookup matches your measurement to that brand's own row. That is why a single measurement can be read against every brand at once, and why a conversion between two brands goes through foot length rather than through a US-to-EU offset.
Sourcing rules
- The brand's own published chart is preferred over any retailer's.
- Where no brand chart is available, at least two independent sources must agree.
- Where sources disagree by more than the precision being claimed, the brand is rejected rather than averaged. Three brands have been rejected on these grounds.
- Sources are listed on every brand page — 122 across the site — so any figure can be checked against its origin.
The trap that catches most size charts
Many brands publish more than one centimetre column, and only one of them is a foot length. The other is a shoe or last measurement, typically running 0.4cm to 1.5cm longer. KEEN, Teva, Mizuno, Dr. Martens and adidas all do this. A chart that quietly uses the wrong column will oversize nearly everyone who reads it.
Children's charts carry a second version of the same trap: some retailers publish figures with growing room already added, then also instruct parents to add growing room. Following both oversizes a child by close to a full size.
Children's sizing
28 of 35 brands publish children's data we could verify. The remaining 7 either publish none, or publish figures that disagree between sources. For those, the calculator uses a standard youth scale and says so on the result rather than presenting it as the brand's own. See the kids' size chart for the full comparison.
Width
8 brands publish genuine width fittings, and those are stored as the brand's own letters rather than normalised, because the letters do not mean the same thing across brands — a D is the standard men's fitting in most American sizing but Danner's wide women's fitting. For every other brand the calculator gives a general estimate and labels it as one. See the width chart.
Rounding and between-sizes
Where a measurement falls between two chart rows, you choose: round up, or take the nearest. Rounding up is the default for children, since feet grow. Where a brand's own chart lists two sizes at the same centimetre — which happens in Nike's, Timberland's and Altra's published charts — the smaller is shown, which is the safer result under a round-up default.
What this cannot tell you
A size chart is a starting point, not a guarantee. Fit varies by model, last, material and how a shoe is laced. Brand charts describe the brand's intent, not any particular shoe. Where a brand's own guidance contradicts its chart — Altra advising extra room, UGG advising to size down because sheepskin compresses — that guidance is shown in the brand's fit notes rather than folded silently into the numbers.
Corrections
Manufacturers revise their charts. Every brand page carries the date its data was last reviewed. If you find a figure that disagrees with a brand's current published chart, please report it — corrections are applied to the source data so every page that uses it updates together.