Why sizes never quite line up
Shoe and clothing sizes grew out of different national systems that were never designed to agree. US and UK shoe sizes both count in barleycorns (a third of an inch) but start from different zeros; EU sizes count in Paris points (two-thirds of a centimetre). Add each brand's own fit adjustments and a "US 9" can genuinely span half a size between manufacturers — which is why every conversion here should be read as the standard mapping, with the brand's own chart as the final word.
PPI vs DPI — not the same thing
PPI (pixels per inch) describes how densely a screen packs its pixels — a 27-inch 1440p monitor is about 109 PPI, a phone can exceed 460. DPI (dots per inch) describes how densely a printer lays ink for a given print size. The same photo has one fixed pixel count but a different DPI at every print size — which is exactly what the Print DPI tab calculates.
Common aspect ratios
Frequently asked questions
How do I measure my ring size at home?
Measure the inner diameter of a ring that already fits, in millimetres, and enter it on the Ring tab. Fingers swell through the day — measure in the evening for the truest fit.
Why does my "US 9" fit differently across brands?
Brands cut lasts (foot forms) differently and round conversions their own way. The chart gets you to the right neighbourhood; the brand's chart gets you to the door.
Is anything saved?
No. All conversions run on your device — nothing you enter is stored or transmitted.