Few purchases are as easy to get wrong as shoes bought across borders. A size 9 in one country is a different size in another, a different size still for the opposite gender, and potentially a different fit in a different brand. The Shoe Size Conversion calculator removes the guesswork from the most important input, your foot length, and turns it into the equivalent sizes for the five major sizing systems used around the world, for adults, kids and infants alike.
Why There Is No Worldwide Shoe Size Standard
Shoe sizing predates mass production by centuries, and the systems it produced never converged. Before factories, a shoemaker built each pair for one customer's foot, so there was no motivation for different regions to agree on a common scale. Countries ended up with different base points, different increments and different ways of naming the same foot. The US, the UK, continental Europe, Japan and China each settled on their own conventions, and those conventions remain today largely because changing them would confuse billions of shoe boxes already in circulation.
Within even a single system, each manufacturer builds its shoes on its own last, the central form around which the shoe is shaped. Two brands can both label a shoe a US size 8 and still differ by a noticeable margin in how they fit the average foot. That is why the calculator is honest about what it does: it converts foot length into the size each system would assign, giving you a reliable starting point, not a guarantee of a perfect fit straight from the box.
How to Measure Your Foot Length
The whole conversion rests on one measurement, so it is worth getting right. Place a sheet of paper on a hard floor against a wall, stand on it with your heel touching the wall, and mark the point of your longest toe. Measure from the wall edge to the mark. Do both feet, because most people have one foot slightly longer than the other, and fit the larger one. Measure in the afternoon or evening, when feet have swollen from walking, since shoes fit best when your feet are at their largest.
Understanding the Five Sizing Systems
The calculator reports sizes in the US/Canada, UK/India, EU, Japan/Mexico and China systems, each with its own logic. The US and UK scales are built from the foot length in inches, with the size growing about three points for every extra inch of foot. The EU scale, often called the Paris point, uses a different base and moves in whole-number steps. Japan and Mexico take the simplest approach of all, quoting the foot length in centimetres directly as the size. China uses its own linear formula and steps up in whole sizes as well.
The Formulas Behind the Conversion
For adults, the US women's size is three times the foot length in inches minus 21, while the US men's size subtracts 22 instead, a difference of a full size between the genders on the same foot. The UK adult scale is close behind, subtracting 23. The EU size is one and a half times the length in centimetres plus two, and the China size is twice the length in centimetres minus ten. Japan and Mexico simply use the centimetre length. The kids and infant scales follow the same structure with adjusted constants, because a child's foot is too small for the adult formulas to make sense.
US women = 3L − 21 · US men = 3L − 22 · UK = 3L − 23 (L in inches)
EU = 1.5L + 2 · China = 2L − 10 (L in cm) · Japan = L
Adults, Kids and Infants Use Different Scales
Pick the sizing group that matches the person the shoe is for. Adult sizes cover both genders and are what most people search for. The kids group, roughly ages five to twelve, uses the big-kid constants, while the infants group for ages zero to four uses an even lower base. Children's feet grow quickly and their shoe sizes change constantly, so measuring each time is especially important for them. A child who needed a size 2 last month may genuinely need a size 3 this month, and no chart can predict that pace.
Entering Your Measurement in Any Unit
Different parts of the world measure feet differently, so the calculator lets you enter the foot length in centimetres, millimetres or inches and converts everything internally to centimetres before applying the formulas. Someone used to the metric system can type 24 cm, a parent with a millimetre ruler can type 240 mm, and a shopper in the United States can type 9.5 inches, and all three get the same set of equivalent sizes back. The final row of the results even shows your measurement in inches for reference.
A Quick Reference for Typical Adult Foot Lengths
The table below shows how common foot lengths map across the systems for women and men on the standard length-based formulas. It is a handy sanity check for the calculator's output: if your 26 cm foot does not come back somewhere in the neighbourhood of these rows, re-check the measurement.
| Foot length (cm) | US women | US men | UK/India | EU | China |
|---|---|---|---|---|---|
| 21.5 | 4.5 | 3.5 | 2.5 | 34 | 33 |
| 23.5 | 6.5 | 5.5 | 4.5 | 37 | 37 |
| 24.5 | 8 | 7 | 6 | 39 | 39 |
| 25.5 | 9 | 8 | 7 | 40 | 41 |
| 27 | 10.5 | 9.5 | 8.5 | 42 | 44 |
| 28.5 | 12 | 11 | 10 | 45 | 47 |
Notice how quickly the China number outruns the EU number for the same foot, because the China formula doubles the length and then subtracts ten, while the EU formula grows more slowly off its own base. That is the clearest visual proof that these systems are not simple offsets from one another, which is why a calculator that works in the underlying foot length is safer than memorised conversion numbers.
Women vs Men: More Than a Number
The US system dedicates separate scales to women and men, with the women's formula running a full size above the men's for the same foot. But the difference is not only numerical. Men's feet tend to be longer and broader, and women's feet differ in shape around the arch, the heel and the forefoot, so a man wearing a women's shoe sized up is unlikely to get a comfortable fit even if the length matches. If you are converting a size rather than measuring a foot, remember the gender switch happens at the source, not just on the label.
Why Fit Depends on More Than Length
Length is where every chart starts and where fit testing actually begins. The width of the foot at its widest point, the height of the instep, the position of the arch and even the circumference around the ball of the foot all change which size works. Few brands standardize width labelling, and many skinny or wide feet simply cannot be matched to a length formula. Foot shape also changes over a lifetime as ligaments loosen with age, which is why a long-time size 9 can slowly become a size 9.5 without the shoe itself changing at all.
How to Measure Like a Professional
Retail shoe fitters use a Brannock device, the metal instrument you step on in shoe stores, which captures length, width and arch length in one go. The RITZ stick was the older wooden version. The Mondopoint system, used widely for ski boots and athletic equipment in Russia, East Germany, Japan, China and South Korea, measures both foot length and width in millimetres to create a two-number size. Any of these measures beats eyeballing a ruler, and if all you have is a ruler, measuring both feet later in the day against a wall is a solid second best.
Practical Conversion Tips
- Enter the length of your longer foot and round the recommended size up when the chart lands between two sizes.
- Expect a half-size gap between adjacent systems; if you sit mid-chart, try the larger option first.
- For children, re-measure before every purchase because growth can shift the size within months.
- If you convert between women's and men's at the same length, remember the US scales differ by one full size.
- Use the calculator for a starting point, then confirm with the brand's own size guide, since each manufacturer adjusts its lasts.
Common Mistakes to Avoid
Measuring the foot while sitting instead of standing inflates the length reading. Measuring only one foot ignores the fact that most people have two different sizes. Relying on a past purchase for a new brand ignores how much lasts vary. And assuming the EU number is just the US number plus a fixed constant fails, because the two systems step at different intervals and move in different increments. Whenever in doubt, go back to the single reliable number: your own foot length.
Converting shoe sizes is only hard because history left so many systems behind. Give the calculator your foot length once, and it returns the size that every major market would put on the box, so you can order from anywhere in the world with a reasonable chance of a fit.
Disclaimer
Results are provided as estimates for informational purposes only and may be inaccurate. Always verify outcomes with a qualified professional before making financial or personal decisions based on these calculations.