The Shoe Size Number on Your Tag Traces to a Grain of Barley from 1324
In 1324, King Edward II issued a decree that established the barleycorn as an official English unit of measurement. The proclamation stated that three round, dry barleycorns laid end to end made an inch. It was a practical choice: barley was abundant, grains were relatively consistent in size, and the unit was familiar to traders across the kingdom. The barleycorn was one-third of an inch, or 8.46 millimeters.
Seven centuries later, that medieval grain is still the foundational unit of British and American shoe sizes. Each shoe size increases by exactly one barleycorn, one-third of an inch, from the previous size. A US men's size 8 is one barleycorn longer than a size 7 and one barleycorn shorter than a size 9. The children's sizing scale runs from size 1 to size 13 and then resets to adult size 1, which is why children's size 13 and adult size 1 exist as separate designations for foot lengths that are nearly identical.
Three major sizing systems exist today, each rooted in a different historical tradition and incompatible with the others. Understanding why they diverge explains why converting between them requires a lookup table rather than a simple formula.
The Barleycorn System and Its Two Versions
The British system, from which the US system descended, set size 1 as 4 inches and increased each size by one barleycorn (one-third of an inch). The size number therefore represents the number of barleycorns above the 4-inch starting point, plus 4 converted to 12 barleycorns. This is why a size 0 does not exist: the smallest defined size is 1, representing 13 barleycorns or approximately 4.33 inches.
When American shoe manufacturers adopted the British framework in the nineteenth century, they made one modification: US men's sizes start from a baseline that is 1 barleycorn longer than the UK baseline for the same size number. A UK men's size 9 is the same length as a US men's size 9.5. The offset is consistent and persistent, having survived more than a century of manufacturing without being corrected or standardized.
Women's sizes in the US system add another offset. US women's sizes are 1.5 sizes larger than US men's sizes for the same foot length. A woman with the same foot length as a man wearing a size 8 wears a size 9.5 in women's sizing. Children's sizes use the same barleycorn increment but count from a different starting point and reset to adult sizing at size 13.
The persistence of these offsets across more than a century reflects how rarely sizing systems, once embedded in manufacturing infrastructure, get corrected. Every shoe last (the foot-shaped mold around which a shoe is built), every grading specification, every retail display system was built around these numbers, and changing them would require coordinated replacement across the entire industry.
The Paris Point and European Sizing
The Paris Point emerged from France's commitment to decimal measurement in the late 1700s, shortly before the metric system was formally adopted. French shoemakers sought a size increment compatible with metric measurement but practical for footwear grading. They settled on two-thirds of a centimeter (6.67 millimeters) as the increment between sizes.
The Paris Point system counts from a baseline of approximately 1.5 centimeters and adds one Paris Point per size, starting with infant sizes and continuing through adult sizes without resetting. Because the French increment (6.67 mm) is smaller than the British increment (8.46 mm), European sizes have more steps over the same range of foot lengths, and European size numbers are larger than UK or US numbers for the same foot.
A UK men's size 9 corresponds to approximately European size 43. But the correspondence is not perfectly linear across all sizes because the starting baselines were set independently, and manufacturers in different European countries have historically rounded up or down at slightly different points. A size 43 from an Italian manufacturer may fit slightly differently from a size 43 from a German manufacturer, not because the size is wrong but because the tolerance allowed within the Paris Point system is wide enough to accommodate minor variation.
The Paris Point system spread across most of continental Europe through the nineteenth century as trade in footwear increased and retailers needed a common standard for imported goods. It was never formally adopted by an international standards body, which means it functions as a de facto standard maintained by industry convention rather than regulatory enforcement.
The Brannock Device and the Measurement Gap
The practical problem with all three systems is that they assign abstract numbers to foot lengths rather than measuring the foot directly. The number tells you where you fall in the sequence of sizes but not what your foot actually measures.
Charles Brannock addressed this limitation in 1925 when he patented the Brannock Device, the metal measuring plate used in shoe stores for decades. Brannock, who worked in his father's shoe store in Syracuse, New York, invented the device to measure foot length, width, and arch length simultaneously. His 1925 patent described a device that produced three measurements and correlated them to a size recommendation. By the 1930s, the Brannock Device was standard equipment in upscale American shoe stores.
The device measures in US size units on one scale and foot length in inches on another, making the conversion between actual measurement and size number visible to the customer. Even with this tool, the recommended size is a starting point. Manufacturers vary in how they cut their lasts, which means a size 10 from one brand may fit like a 10.5 from another even when both claim to follow the same sizing standard. Research surveys of footwear fit conducted by shoe manufacturers and retailers consistently find that 30 to 40 percent of people are wearing the wrong shoe size, often a size too small.
The Asian Centimeter Standard
Japan, South Korea, and several other Asian countries use a system that bypasses abstract size numbers entirely. Shoes are labeled in centimeters of foot length, so a size 270 means a shoe designed for a 27-centimeter foot. Half-centimeter increments are common, so sizes proceed as 255, 260, 265, 270, and so on.
This system has the advantage of direct measurement correspondence. If you know your foot is 26.5 centimeters long, you look for a size 265. There is no memorized offset or baseline to account for, no gender correction, and no children's reset. The size number directly communicates the foot length it accommodates.
The tradeoff is that the system handles width differently. Many Asian sizing standards include a width code (A, B, C, D, E, EE) alongside the length measurement, where E and EE indicate wider fits. UK and US systems also have width designations (A through EEEE), but these are rarely marked on consumer shoes in those markets. Asian market shoes are more likely to include explicit width information, which makes fit prediction more reliable.
Conclusion
Converting between shoe size systems requires lookup tables rather than formulas because the three systems do not have a clean mathematical relationship. The UK/US barleycorn increment (8.46 mm) and the Paris Point increment (6.67 mm) are not multiples of each other. The starting baselines were set independently. US men's and women's sizes have different offsets from UK sizes. Children's sizes in different systems stop and reset at different points.
The result is that conversion charts must list each size pair individually rather than applying a single formula. A published conversion table from a major footwear manufacturer may show UK 9 = EU 43 = US 10, but another manufacturer's chart may show UK 9 = EU 43 = US 9.5 because they apply the gender offset differently. Both are internally consistent with their own baseline choices.
For online shopping across international retailers, the safest approach is to measure foot length in centimeters and use the Asian standard as a reference, since it eliminates the offset problem. The ToolHQ shoe size converter translates between all major systems using standard reference tables, giving you the most common equivalent for each size in each system.
Frequently Asked Questions
Why do shoe sizes go from children's 13 back to adult size 1?
Because both scales start from the same baseline and count upward in barleycorn increments. After children's 13 reaches a certain foot length, the adult scale restarts at 1 from its own baseline, which happens to produce nearly the same foot size.
What is a Paris Point in shoe sizing?
A Paris Point is two-thirds of a centimeter, the increment used in continental European shoe sizing. Each European size is one Paris Point longer than the previous, making EU sizes incompatible with US or UK sizes except by lookup table.
How do Japanese shoe sizes work?
Japanese shoe sizes use the foot length in centimeters. A Japanese size 27 means a foot 27 centimeters long. This is the most literal system, but it still requires a conversion table to compare against US or EU sizing.