Methodology

Last reviewed 2026-07-28.

How the tables are built

Every conversion table on SizeDecoder is compiled from standard, widely published sizing conventions for each garment category — the same reference points used by apparel-industry sizing standards and long-established retailer conversion charts, cross-checked against more than one source rather than copied from a single retailer's page. Where two respected sources disagree by a fraction of a size (common in shoe sizing, where the US-to-EU relationship in particular has never been perfectly linear), we use the midpoint value that's most commonly cited and note the spread on the relevant chart page rather than presenting false precision.

Why every table is "general guidance"

No clothing or shoe sizing system in current use is a fixed, regulated standard the way a unit of length is. Shoe-size systems were built around different last-measuring conventions (the English "barleycorn" system, the French Paris-point system, and the Mondopoint foot-length-in-millimeters system all measure genuinely different things). Clothing sizes are set independently by each brand's own pattern-making, and "vanity sizing" — labeling garments smaller than their actual cut to flatter the buyer — has measurably drifted mainstream US numeric sizing over decades. That means a size conversion is always an approximation of where a garment or shoe is likely to sit, not a guarantee. We say so on every conversion and chart page, and we link to how to measure yourself so you have a second, independent check.

Dating and updates

Sizing conventions change slowly, but they do change — most notably as national and regional standards bodies periodically revise size-label recommendations. This page's "last reviewed" date above reflects when the underlying tables were last checked against current published conventions. If you find a chart that looks meaningfully out of date or contradicts a garment's own labeled size chart, the garment's own chart wins — please let us know so we can check it.

What we don't do

We don't scrape a single brand's chart and present it as universal, and we don't fabricate a false level of precision (a "37.5" EU shoe size, for instance, is a real half-size some brands use and others skip — we show it where it's genuinely part of that brand family's convention, not as a rounding trick).

How sourcing differs by category

Not every garment type has the same quality of underlying standard, so the confidence behind each chart varies by category rather than being uniform across the site. Shirt collar, glove, and hat sizing are the most reliable, since all three are genuine unit conversions of an actual body measurement (neck, palm, or head circumference) rather than a coded scale — the arithmetic behind them doesn't drift the way a coded number can. Ring sizing sits in the middle: the underlying circumference-to-size relationship is well standardized across jewelers, but which of three genuinely different labeling conventions (US number, UK letter, EU millimetre diameter) a specific retailer uses still needs checking. Shoe and clothing sizing carry the least certainty of any category here, since both are shaped by brand-specific vanity sizing and last or block shape on top of the nominal conversion — which is why every shoe and clothing chart on this site repeats the same advice to check the specific brand's own numbers.

How disagreements between sources get resolved

When two respected references disagree on a specific conversion point, we don't average them silently. For shoe sizing, where the US-to-EU relationship has never been perfectly linear across the full size run, we favor the value most commonly published across multiple independent retailer charts for that size, and flag on the relevant chart page where the disagreement is wide enough to matter (typically at the smallest and largest ends of a size run, where a single Paris-point step can round differently). For bra cup lettering, where the US convention historically stops earlier than the UK or EU alphabet, we show the honest gap rather than inventing a US letter that doesn't have real market consensus behind it.

Review cadence

Categories built on a genuine physical unit (shirt collars, gloves, hats, ring diameters) need the least frequent review, since the underlying arithmetic doesn't go stale. Shoe and clothing charts are reviewed on a shorter cycle, since brand-level vanity sizing and national standards guidance can shift over a period of years in ways a unit conversion never does. If a specific chart hasn't been reviewed in longer than that category's typical cycle, the "last reviewed" date above will lag, and that's a signal to treat the table with slightly more caution and check the garment's own chart directly.

Why the same size number sometimes points to two figures

A handful of garment categories genuinely have more than one live convention behind the same-looking number, and we try to be explicit about which one a chart is using rather than quietly picking one. Kids' clothing sizing is the clearest example: a size labelled by age is really an assumption about typical height and weight for that age, not a direct measurement, so this site's kids' charts show the underlying height band alongside the age label wherever the source data supports it, rather than presenting the age number as if it were as precise as an adult chest or waist measurement.

Combinatorial coverage: essential versus reference pairs

The conversion section of this site covers every region pair for every garment we publish a chart for, which produces a genuinely large number of individual pages. Rather than write the identical depth of brand-specific nuance on every single pair — which would mean padding out less-searched pairs with filler rather than real research — the highest-demand pairs (the ones with a real, well-documented fit quirk behind them, like US-to-EU shoe sizing or the three genuinely different physical quantities behind ring sizing) get full researched explanations. The rest of the region-pair combinations for each garment ship as a direct, accurate conversion table with a short, pair-specific note and a link to that garment's full chart, which carries the deeper explanation once rather than repeating it dozens of times with the country names swapped.