Shoe Size Conversion

What each shoe size system measures

Every shoe size system describes a length, but the systems disagree about three things: what the number measures, what the number zero means, and how much a step between sizes covers. The result is that a US 9, a UK 8 and an EU 42 can all be the same shoe, and a size printed on a box is meaningless without its system.

Mondopoint, defined in ISO 9407, is the only system that measures the foot itself. The European and UK systems measure the last, which is the wooden or plastic form the shoe is built around, and the last is longer than the foot by roughly 13 to 17 mm. That is why a shoe labelled EU 42 fits a foot that is about 26.7 cm long, and why the number on the box is larger than the measurement you take at home.

Sneakers sold in the United States often print a centimetre number such as 26.5, which is a Mondopoint size written in centimetres rather than millimetres. A sports shoe box with three systems on it is following the same habit, just with more labels.

The conversion formulas behind the chart

Converting between systems works best when every size is routed through the foot length in millimetres. That is the approach the ISO 19407 technical specification takes, and it is the one this page and the converter above both use.

For a foot length L in millimetres, the European size is 0.15 x L + 2. A foot of 254 mm gives 0.15 x 254 + 2 = 40.1, which the chart prints as EU 40.

The UK size is 3 x L / 25.4 - 23, where 25.4 is the number of millimetres in an inch. The same 254 mm foot gives 3 x 254 / 25.4 - 23 = 7.

The US sizes sit on top of the UK scale. A US men size is one step above UK, and a US women size is two steps above UK, so a 254 mm foot is US men 8 and US women 9. Mondopoint is the foot length itself, 254 mm for that same foot. Every row of the adult table below comes from these five lines.

Because the tables round to the size a foot fits, the printed result is the nearest half size rather than the raw formula output. When a measurement lands between two sizes, take the larger one, since a shoe that is half a size tight is a shoe you will take off.

Adult conversion table

This table covers the adult range most people shop in. Each row is one foot length, expressed in every system, with the US men and US women columns sitting above the UK number.

Read across a row rather than down a column when you are checking a pair of shoes. A box marked EU 42 usually carries UK 8 or UK 8.5 next to it, because the two scales drift apart as sizes grow, so the safest check is to find your foot length in the first column and read your own system across the same row.

Two habits make the chart easier to use. Measure your foot in the evening, when feet are at their largest, and add nothing on top of the chart. The extra room is already built in, and adding your own allowance is the most common reason a correctly converted size still feels wrong.

Worked example: a 27 cm foot

Take a foot that measures 270 mm from heel to longest toe, which is a common size for an adult man or a tall adult woman.

The European size is 0.15 x 270 + 2 = 42.5. The UK size is 3 x 270 / 25.4 - 23 = 8.89, which rounds to 9. US men is one step above UK, so 9.89 rounds to 10, and US women is two steps above UK, so 10.89 rounds to 11. Mondopoint is 270, and the same length in inches is 270 / 25.4 = 10.63 in.

So a 27 cm foot is EU 42.5, UK 9, US men 10, US women 11, Mondopoint 270, or 10.63 inches. Put the same foot into the converter at the top of the page and you get those seven numbers back.

Notice how the gaps behave. Moving up one UK size adds 8.47 mm of foot length, and moving up one EU size adds 6.67 mm. That is why a European size rises faster than a UK size for the same person, and why sizes in different systems do not line up one for one.

How to measure your foot at home

You need a sheet of paper, a wall, a pen and a ruler, and about two minutes. Stand on the paper with your heel against the wall, weight on both feet, and mark where your longest toe ends. Measure the distance from the wall to that mark. Repeat with the other foot and use the longer result, since most feet are not identical.

Measure in the evening rather than the morning, and wear the socks you would wear with the shoes. Feet swell during the day, and a measurement taken early can be a half size light by evening. If you are between sizes, take the larger one.

Do not add a length allowance on top of the chart. The 13 to 17 mm between foot length and last length is already reflected in every size in the table, and adding your own allowance on top of it is how people end up two sizes too big.

Children's sizes and a different zero point

The EU formula still works for children, because it starts from foot length. The UK and US children's scales do not, because their zero points are different. UK child size 0 fits a foot of about 8.3 cm, and US child sizes run half a size above UK, so a 12 cm foot is UK child 4 and US child 4.5. The adult formulas would give a negative number for those feet, which is the quickest way to see that a different scale is in play.

Children's feet grow in spurts rather than smoothly, and a growth spurt can add more than a size between two shopping trips, so leave room and remeasure rather than buying to the current number. The converter on this page deliberately covers adult feet from 21 cm to 33 cm only, and it tells you when an input falls outside that range.

Why one size fits differently across brands

A conversion gives you a starting point, not a guarantee. The ISO specification itself notes that shoe size systems were developed locally and interpreted differently for decades, and that its tables are a good compromise for shoppers rather than an exact translation. Brands also build their lasts to a different shape, so two shoes both labelled US men 9 can have different internal widths.

US width letters describe the width of the last, and they matter more than most shoppers expect.

US width letters do not transfer cleanly to European labels, where a German D, a French D and a British G can sit on different width scales. When a brand publishes its own width chart, that chart beats any conversion table, including this one.

Width, arch and the limits of a length chart

Length is the part of a shoe that is standardised. Width, arch height and overall volume are not, and they are the reasons a correctly converted size can still pinch. A foot with a high instep needs volume rather than length, and a high instep is often the reason a size has to go up even though the length fits. A 3D scan of the foot, or an insole print, catches what a tape measure cannot.

Two practical rules cover most cases. Running shoes and sneakers are usually worn half a size up from the dress shoe size, because a foam midsole needs room and because feet swell on a run. Dress shoes and heels are usually worn true to size, because the shoe is built to hold the foot rather than cushion it. ISO 19407 holds the conversion tables behind this page, and the NIST general tables of units hold the exact conversion of 1 inch to 2.54 cm that every formula here relies on.

For the widest range of adult sizes in one place, the shoe size overview lists the size marking tables from ISO 19407, including the children's chart used above. When a brand's own chart and a conversion disagree, the brand's chart wins, because it describes the shoe in your hands.