How We Source Size Data
SizeFit publishes converters and charts so you can turn a size you know into another label—or match a measurement in cm or inches. This page explains where those numbers come from, how often we re-check them, and what we do not invent.
Last reviewed October 5, 2026. Airline bag limits use a separate process—see how we verify baggage data.
Source priority
- Brand size guides — Nike, adidas, New Balance, Gap, and similar published charts when the page is about that brand.
- Standards — e.g. Mondopoint / ISO 9407:2019 for foot length in mm, ISO 19407:2023 for conversion tables, ASTM crib mattress footprint notes when a standard applies.
- Common retail footprints — US Twin / Full / Queen / King mattress and bed-blanket inches that most North American retailers use. Brands can still print different inches on the package.
If an official page is unclear or missing a field, we leave a gap or mark the row as approximate—we do not invent a fake “official” number.
What the converters do
- Generic shoe rows bridge US / UK / EU using foot length in cm as the shared scale.
- Brand shoe and apparel tables follow that brand’s published guide when we have it in our data files.
- Clothing letter sizes still vary by cut—body measurements beat guessing from “M” alone.
- Fit tips (for example “Air Force 1 often runs 0.5 large”) are shopper patterns, not a warranty that every pair fits that way.
How often we re-check
We aim to review each size category about every 180 days, or sooner when a brand publishes a new guide or readers flag a wrong row. Pages that show Last verified use the date from our authority log for that category.
- Open the brand or standard page linked in Data Sources.
- Compare US / UK / EU / cm (or inches) rows to our table.
- Update the data file and the verified date when something changed.
Category status
Current verification snapshot for non-airline charts and tools:
| Category | Last verified | Review cycle | Sources listed |
|---|---|---|---|
| Shoe size charts & converters | 2026-10-05 | 180 days | 5 |
| Nike shoe size chart | 2026-10-05 | 180 days | 2 |
| adidas shoe size chart | 2026-10-05 | 180 days | 2 |
| Bra size charts & calculator | 2026-10-05 | 180 days | 2 |
| Ring size charts & converter | 2026-10-05 | 180 days | 2 |
| Hat size charts & converter | 2026-10-05 | 180 days | 2 |
| Clothing & pants size charts | 2026-10-05 | 180 days | 3 |
| Mattress, blanket & sheet sizes | 2026-10-05 | 180 days | 2 |
| At-home measurement guides | 2026-10-05 | 180 days | 2 |
- Shoe size charts & converters: Generic rows follow common Mondopoint / cm bridges used by major retailers; brand tables come from each brand’s published size guide.
- Nike shoe size chart: US / UK / EU / CM rows mirror Nike’s published size guide. Fit notes (e.g. Air Force 1) are common shopper patterns—not Nike’s official claim for every model.
- adidas shoe size chart: US / UK / EU / CM rows follow adidas published size charts, including fractional EU steps (42 2/3, 43 1/3). Ultraboost fit notes are shopper patterns, not a model-by-model warranty.
- Bra size charts & calculator: Band numbers follow underbust; cup letters follow bust-minus-underbust. US / UK / EU label maps are a starting point—cup letters after D and brand stretch still vary.
- Ring size charts & converter: Rows map inside diameter and circumference in mm to US numbers, UK letters, and EU circumference labels. Jewelers can still round differently—confirm with a physical sizer.
- Hat size charts & converter: Fitted fractions (7, 7 1/4, 7 3/8) follow head circumference in inches/cm used on New Era–style tags. Flexfit and snapbacks use letter or adjustable ranges—confirm the product tag.
- Clothing & pants size charts: Label conversions use published brand charts where available; body-measurement tools prefer inches/cm over guessing from one letter size.
- Mattress, blanket & sheet sizes: US bed footprints (Twin through King / Cal King) follow common North American retail standards. Blanket and sheet inches can vary by brand—always check the product label.
- At-home measurement guides: Steps are practical methods used by retailers and fit guides (trace foot, tape body). Converted sizes still depend on each brand’s chart.
How to cite SizeFit
Prefer linking the specific chart or converter URL (each page shows Cite this page with a stable address). Name the verification date you saw on that page. For airline dimensions, cite the airline’s own policy page as the primary source and SizeFit as a comparison helper.
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