Why UK, US and EU never quite agree
Three separate systems grew up in three separate places, and none of them were designed with the others in mind. British sizing counts in barleycorns, an old unit equal to a third of an inch. American sizing borrowed the same barleycorn step but started counting from a different point, and split into a men's and a women's column along the way. European sizing ignores inches altogether and counts in Paris points, two-thirds of a centimetre apiece, on a single scale that runs unbroken from a baby's first shoe to an adult's largest. A UK size and a US size can describe the same foot with two different numbers for the same reason a UK size and an EU size can: they were never the same ruler to start with.
None of that would matter much if every shoemaker measured against the numbers with total consistency, but they do not. A last, the foot-shaped form a shoe is built around, is a design choice a brand makes for itself, and two brands' size 9s can differ by a visible margin even when both claim the same UK, US or EU chart underneath. Treat every size label here, and everywhere else, as a very good estimate rather than a guarantee, and lean on the foot length figure when a fit really has to be right first time.
Grains of barley and a king's decree
The barleycorn behind UK sizing is not a metaphor. English statute once defined the inch itself as three dried grains of barley laid end to end, a rule recorded from the thirteenth century and formalised under Edward II in 1324. Shoemakers adopted a third of that inch, one barleycorn, as the gap between consecutive sizes, and the practice has stuck for seven centuries: British sizing still moves in exact thirds of an inch today, half a barleycorn for a half size.
The two UK formulas above share the same barleycorn step; only the starting point differs, because a baby's first-shoe scale and an adult scale cannot both start counting from zero at the same foot length. The gap between the two constants, 13, is exactly the size difference at which children's numbering hands over to adult numbering on many British charts.
Why the US number jumps by one, or two
US sizing kept the barleycorn step but shifted where the counting starts, and shifted it differently for men's and women's lasts. The convention used on this page, and on many published charts, adds one full size to get from UK to US men's, and two full sizes to get from UK to US women's:
Not every retailer uses that exact offset. Some charts shift US men's sizing by only half a size against UK, and children's US and UK numbers sit within a quarter size of each other rather than a whole one. This is the genuinely messy part of shoe sizing: two perfectly legitimate charts can disagree by half a size for the same reason two brands' lasts disagree, and the foot length in centimetres is the figure that stays put while the labels around it move.
One European scale, start to finish
EU sizing measures in Paris points, two-thirds of a centimetre apiece, and never resets. The same formula that converts an adult's foot length to an EU size also converts a toddler's, which is why an EU size on its own tells you nothing about which country's chart it came from, only how long the last was built for.
Because it runs continuously, EU sizing is often the steadiest reference point between a children's chart and an adult chart when a growing foot sits near the boundary between the two.
Width is the part no size chart shows
Every number on this page describes length alone. Foot width is its own measurement, usually shown as a letter, narrow through wide: A, B, C, D, E, EE and sometimes wider still, though the letters do not mean quite the same width in every country's system. A shoe that measures right in length but comes up tight across the ball of the foot is very often a width problem, not a size problem, and no length-only calculator, this one included, can fix that from a single number. Brands that offer named width fittings are worth seeking out if a standard width consistently pinches or gapes.
Buying a size you have never tried on
Foot length in centimetres is the only figure on this page that travels reliably between brands, which makes it the safest thing to check before buying a shoe you cannot first put on. Most footwear retailers publish their own size chart with a foot-length column; matching your measured length against that specific chart, rather than trusting a size number carried over from a different brand, avoids the single most common online sizing mistake. Where a chart offers a choice between two adjacent sizes, the general rule for everyday shoes is to size up rather than down, since a shoe that is briefly loose is more forgiving than one that is genuinely too short.
Children's sizes move fast, and the numbers are rougher
An age next to a shoe size is always a guide, never a measurement. Children's feet grow at very different rates, commonly a size every two to three months through infancy and every three to six months at school age, so the age brackets on the chart below are rough by design and worth checking against an actual foot length rather than a birthday. This tool covers sizes from roughly six months to six or seven years old; once a child's feet reach the top of that range, the following size is usually labelled on the same numbering used for small adult sizes, so the men's or women's category above picks up where the kids' category leaves off.
Questions people ask
Why do UK, US and EU sizes not just use one system?
They grew up independently. UK and US sizing both trace back to the barleycorn, a third of an inch per size, but started counting from different points and, for the US, split into separate men's and women's columns. EU sizing abandoned inches for a metric step, the Paris point, and never adopted the others' numbering at all.
Is US men's size really UK plus one?
On many widely published charts, yes, and that is the convention this page uses. Other charts shift US men's sizing by only half a size against UK instead. Both are genuinely in circulation, which is exactly why checking foot length in centimetres against a specific brand's own chart beats relying on a size number carried over from somewhere else.
Why is EU sizing the same scale for children and adults?
Because the Paris point formula behind EU sizing is one continuous line rather than two separate scales stitched together. A size 30 is simply whatever foot length that formula says it is, whether the foot belongs to a young child or a small adult, which is why EU numbers alone do not tell you which age group a shoe was cut for.
How much room should I leave beyond my measured foot length?
Roughly 1 to 1.5 cm past the longest toe for an adult shoe, a little less for a young child's growing foot, around 0.8 to 1.4 cm. This calculator's size figures already assume a normal amount of that allowance is built into the chart; add extra room only if you know a particular last runs short.
What if my foot measures between two sizes?
Round up rather than down for an everyday shoe. A slightly loose fit is usually solved with a thicker sock or an insole; a shoe that is genuinely too short rubs and cramps toes with no equally easy fix.
Do width fittings change what number I should buy?
Not the length number, but they change whether that length actually fits comfortably. Width is measured separately, usually as a letter from narrow to wide, and a shoe that is the right length but the wrong width is a common source of a fit that never quite feels right.
Why do two pairs in the same labelled size fit differently?
Because the size label describes an intended last, not a fixed physical measurement, and lasts differ between brands and even between styles from the same brand. A size that fits perfectly in one pair is a reasonable starting point elsewhere, not a promise.
Sizes here follow published barleycorn and Paris-point formulas, cross-checked against several retail conversion charts. Individual brands and styles can and do differ from any chart, including this one, by up to a full size.