Shoe Size Converter Explained

What a shoe size actually measures

A shoe size is a code for the internal length of a shoe last — the wooden or plastic mould that a shoe is built around. The number on the box is not the length of your foot; it is the length of the last, which is a few millimetres longer to leave room for toe splay, socks, and the natural forward slide of the foot inside the shoe. The shoe size converter on Calc Dragon turns any adult US, UK, EU, or Japanese size into the equivalent in every other region, plus a physical foot length in millimetres so you can sanity-check against a tape measure.

Four systems dominate the adult market. The US and UK scales are both anchored on the Brannock Device, invented in 1927 by Charles Brannock and still the reference tool sitting inside almost every US shoe shop. The European scale uses Paris points — a survival from nineteenth-century French shoemaking. Japan writes size as a foot length in centimetres, an implementation of the ISO Mondopoint standard. Learning how they connect is mostly a matter of remembering four small offsets and one large caveat: brand variance of half a size or more is normal.

The four scales, one Brannock at the centre

Every shoe last has a length, and every scale is a different way of labelling that length. Once you see them all as lengths, the conversions become obvious.

US: 1 size = 1/3 inch of last length

The US Brannock system defines a full size as one-third of an inch, or 8.47 mm, of last length. A half size is 4.23 mm. There are separate men’s and women’s scales because women’s lasts are proportioned differently — narrower at the heel, slightly different arch geometry — even at the same length. The two scales are offset by 1.5 sizes: a women’s US 8.5 has the same internal length as a men’s US 7.

UK: 1 size = 1/3 inch, but numbered lower

The UK scale uses the same 1/3-inch step as the US, but its zero point is different. A men’s UK 0 is a shoe with a 4-inch internal last length (a very small child’s shoe); each subsequent full size adds 1/3 inch. The upshot is that UK sizes come out 0.5 below US men’s and 2 below US women’s for the same last. A men’s US 10 is a UK 9.5; a women’s US 7 is a UK 5.

EU: Paris points, unisex

The European scale is defined in Paris points, where one point equals two-thirds of a centimetre (about 6.67 mm). The number on the box is the last length in Paris points. Critically, there is one EU scale, not a men’s and women’s split — a "size 42" box is the same box whether it holds a men’s Oxford or a women’s loafer. That is why EU and Japanese sizing is often preferred for online orders across the men’s/women’s boundary.

Japan / Mondopoint: foot length in centimetres

Japan adopted the ISO/TS 19407 Mondopoint standard as its national system. Mondopoint expresses size as the actual foot length in millimetres, rounded to a 5 mm grid, sometimes with a width designator like C, D, or E. Japan writes the same number in centimetres on the box, so 250 mm becomes "25.0." Of the four scales, this is the only one where the number on the box is directly meaningful in physics: it is your foot length. If you can measure your foot with a ruler, you can buy shoes in Japan without a chart.

The conversion formulas

Within the standard adult range, the offsets are stable enough to write as arithmetic:

• Men’s / unisex: UK = US − 0.5, EU = US + 33, JP (cm) = US + 18
• Women’s: UK = US − 2, EU = US + 31, JP (cm) = US + 17

These are the offsets the shoe size converter uses internally, and they match the published Brannock charts and the cross-reference tables that Nike, Adidas, Clarks, and most major retailers publish. The men’s/women’s split of 1.5 sizes appears again if you compare the US columns: a men’s US 8 and a women’s US 9.5 both convert to an EU 41 and a JP 26 cm. That is not a rounding artefact — it is the real 1.5-size gender offset made visible.

Worked example: buying trail runners across regions

Say you normally wear a men’s US 10 in road trainers and want to order a pair of Salomon trail runners from a European retailer, with a backup pair from a Japanese seller. Feed a men’s US 10 into the shoe size converter:

• US men’s 10 → UK 9.5 → EU 44 → JP 28.0 cm
• Estimated foot length: 280 mm ≈ 11.02 in

The European retailer will list EU 44. The Japanese seller will list 28.0 cm. If you order both and measure them at home, the internal length of both lasts should land within about ±3 mm of each other, because they were built to the same Brannock-aligned target. Any bigger difference than that is brand variance, and Salomon in particular is known to run about half a size small across their trail range — a data point worth checking on the maker’s size chart before you commit.

The same procedure works the other way. A women’s EU 39 you spotted in Zara? The converter reads across to US women’s 8, UK 6, JP 25.0 cm, foot length ≈ 250 mm. If your measured foot length is closer to 245 mm, the EU 39 will probably be half a size loose, and you can either check for a Zara EU 38.5 or size down. For a full mm-to-inches unit sanity check on any measured foot length, the distance converter covers every step of the way.

Factors that affect the fit beyond the number

Brand variance is half a size, sometimes more

Even within a single region and gender, the same nominal size varies between brands. Converse Chuck Taylors are famously about half a size large — a Converse US 10 fits closer to a US 10.5 in other brands. Nike running shoes are about half a size small. European fashion brands with narrow lasts (Prada, Bottega Veneta, Dior) often need one full size up from your standard sports fitting. Athletic brands with a wider last (New Balance, Altra) can go the other way. The number on the box is a starting point, not a promise — if you are picking running shoes for a specific training block, the pace converter is a useful follow-on tool for matching a shoe’s intended pace range to your target zone.

Width matters, and most scales ignore it

The four base scales all encode length; none of them encodes width by default. US and UK sizes optionally add a width letter (D is standard men’s, B is standard women’s, EE is wide, 2E is very wide). Mondopoint uses letter suffixes (C, D, E, F, G, H) for the same purpose. If you have a wide foot and only a length number to work with, size up half a size — you are trading a slightly loose length for enough forefoot volume, which is usually the better compromise.

Foot volume, not just length

Two feet with the same length can have very different volumes. High arches, prominent big-toe joints, and thick metatarsal pads all raise volume. A shoe that fits your length perfectly can still crush the top of your foot if the last is low-volume, and that discomfort will not show up until an hour of walking. When buying online, look for reviews that mention volume or "toe box height" — length alone will not surface this.

Feet swell during the day

Adult feet gain roughly 4–8% in volume between morning and evening, and that can move you up half a size by the end of the day. Retail shoe fitters have known this for a hundred years, which is why serious fitting sessions happen in the afternoon. If you are measuring at home to feed the shoe size converter, do it in the evening, standing up, weight on both feet.

The two feet are not the same length

Most people have a length difference of 3–8 mm between left and right foot. If yours differ by more than half a Mondopoint step (5 mm), fit to the larger foot and use an insole or heel grip in the smaller shoe. Ordering to the shorter foot will guarantee a long-term problem — cramped toes on one side and a slow deformation of the shoe as your longer foot forces itself in.

How to measure your foot properly

The most reliable way to use any conversion table is to skip the original size entirely, measure your foot, and read the Mondopoint column directly.

• Do this in the evening, after a normal day on your feet — you want the swollen, in-use foot length, not the morning number.
• Stand on a sheet of A4 or letter-size paper with your heel touching a wall. Weight evenly on both feet. Do not lift your heel to check.
• Have someone mark the tip of your longest toe. That is often the second toe, not the big toe. Do it for both feet.
• Measure from the wall edge of the paper to the mark, in millimetres. Take the longer of the two feet as your working number. If you only have a ruler in inches, the distance converter will turn it into millimetres cleanly.
• Add 5–10 mm of toe room for a comfortable shoe fit — closer to 10 mm for running shoes, closer to 5 mm for a dress shoe or a climbing shoe.
• Look up the result in the JP / Mondopoint column of the shoe size converter. Read across to see the size number every other region would print on the box.

Common mistakes when converting sizes

Assuming men’s and women’s scales are interchangeable

In the US and UK they are not. The 1.5-size offset is a real difference in last geometry. A women who wears a US 8 who reads her partner’s men’s US 9 sneaker as "close enough" will get a shoe that is nominally half a size long but also proportioned for a different heel-to-forefoot ratio, and it will slip at the heel. In EU and JP sizing the number is unisex, so the same misreading does not happen — a Zara EU 40 is a Zara EU 40 for anyone.

Trusting a single retailer’s chart over the standard

Retailer charts drift over time and sometimes round in surprising directions. If the retailer’s chart says a women’s US 7 is an EU 37 but the standard mapping (US 7 → EU 38) says otherwise, do not assume the retailer is right. Measure your foot in millimetres, use the Mondopoint column, and let the physical length settle the disagreement.

Forgetting sock thickness

A thick winter sock adds 3–5 mm of packing around the foot, which shows up as roughly half a size of apparent length. A running shoe fitted with a thin synthetic sock will feel different in a thermal wool sock. If the shoe is destined for one specific sock, fit it in that sock.

Sizing children’s shoes off adult charts

Kids’ shoe scales run on separate numbering that resets at the child / youth / adult boundary. A UK 13 kids is smaller than a UK 1 adult. Do not use the adult shoe size converter for children — use a kids-specific chart, or measure the foot in millimetres and use the child’s Mondopoint size directly. Kids’ lasts are also proportionally wider than adults, which is why the number does not simply extend downward.

When a conversion is not enough

For diabetic footwear, custom orthotics, post-surgical rehabilitation, or any shoe worn every day for a working shift, a chart is not enough. Book a proper fitting at a specialist retailer with a Brannock and, if possible, a 3D foot scanner. The scanner captures volume, arch height, and asymmetry that no two-number size code can express, and a fitter can steer you toward brands whose lasts match your foot geometry rather than force your foot into a size number. This article and the calculator are designed for the ordinary case — buying a pair of trainers online, checking whether the EU 42 that came up cheap will fit, moving countries and needing to work out your new local size.

Frequently asked questions

Why are men’s and women’s scales different in the US and UK?

The Brannock Device was designed with separate scales because adult women’s and men’s feet at the same length differ in heel width, arch position, and toe box proportions. The 1.5-size numerical offset (women’s US 8.5 ≈ men’s US 7) is a labelling convention that also flags the geometric difference. EU and Japanese sizing skip the split because they only encode length, leaving fit differences to width designators and last shape.

What is Mondopoint and why is Japan on centimetres?

Mondopoint (ISO/TS 19407) expresses shoe size as the internal last length in millimetres, on a 5 mm grid, with an optional letter for width. Japan adopted Mondopoint as its national standard and prints the millimetre figure in centimetres — so 250 mm becomes "25.0" on the box. This makes Japanese sizing the most physically meaningful of the four scales.

How much do brands vary from the standard?

Within a single region and style, brand-to-brand variance of half a size is very common. Converse runs about half a size large; Nike running shoes about half a size small; narrow-fit European brands (Dior, Bottega Veneta, some Prada lines) can need a full size up. Use the calculator as your starting point, then check the brand’s own chart before you commit — especially if the shoe is non-returnable.

My left and right foot are different lengths. Which one do I size to?

The larger. Almost everyone’s feet differ by 3–8 mm, and sizing to the smaller foot guarantees the larger one will cramp. Add a heel grip or a thin insole in the smaller shoe if the fit feels loose. If the difference exceeds a full Mondopoint step (5 mm), a specialist retailer can sometimes sell you a split pair.

Does this work for kids’ sizes?

No. This calculator and article cover the adult range — roughly men’s US 5–14 and women’s US 4–12. Kids’ UK and US sizes reset at the child / youth / adult boundary and are proportioned for a wider, higher-volume child’s last. Use a kids-specific chart, or measure the foot in millimetres and use the child’s Mondopoint size directly.

Why do I see two different EU sizes for the same US size on different sites?

The EU scale is defined in Paris points (2/3 cm each), and the step between EU sizes is not a whole number of US sizes — the offset drifts by half a point every couple of sizes. Retailers round it differently. The shoe size converter uses the widely-cited Brannock-aligned mapping (EU = US + 33 for men’s, US + 31 for women’s), which is what Nike, Adidas, and most large retailers publish. A one-point discrepancy versus a specific brand’s chart is normal.

What if my measured foot length sits between two Mondopoint sizes?

Round up. Shoe lasts are generous downward — a 253 mm foot in a 255 mm Mondopoint shoe will feel snug but fine, while a 253 mm foot in a 250 mm shoe will jam the toes. If you are between sizes, take the larger size and, if needed, tighten the fit with a thicker sock or an insole. This is why the standard wisdom is "when in doubt, size up."

Does the calculator handle EU half sizes?

EU sizing includes half sizes (39.5, 40.5, etc.) in some brands and regions, especially in athletic and running shoes. The calculator’s conversion is a linear offset, so a half step in one region maps to a half step in another. In practice, whether the specific EU half size exists depends on the brand — some run whole sizes only, some go by half sizes, and a few run in Mondopoint-native 5 mm steps regardless of the printed EU number.