From foot length to size
Each size system is a table of sizes and the longest foot each size fits. Your size is the first one that fits a foot at least as long as yours, so a foot between two sizes is always rounded up, never squeezed into the smaller one. When your foot is within 1.5 mm of the smaller size’s limit, the result says so: that size may fit too, depending on the shoe.
Measure the longer of your two feet, from the back of the heel to the tip of the longest toe. Typed lengths can be in centimetres, millimetres or inches; the shoe size calculator takes any of them.
Measuring with a photo
The camera uses the sheet of paper as its ruler. A sheet of A4 is 210 × 297 mm and US Letter 215.9 × 279.4 mm, so once its four corners are found in the photo, every point on the paper has a known position in millimetres. All of this runs on your device; the photo is never uploaded.
- It finds the sheet’s straight edges and corners, even where your leg hides an edge, and corrects for the slight bend a phone’s lens puts in straight lines.
- It flattens the photo to a top-down view of the sheet, 5 pixels to the millimetre.
- It learns how the light falls across the bare paper, then marks what isn’t paper: your foot.
- Length is from the wall edge of the sheet to the furthest toe; width is the widest part in the front 40% of the foot.
- The outline of a foot isn’t flat on the paper, and the phone sees it from an angle. From where the camera was, it works out where the outline really is.
When it finds the paper itself, it checks before showing a number that the paper is flat, its end at the wall in view, the photo bright enough, the toes inside the sheet and the shape a foot’s. If anything is off, it asks for another photo and says what to change. You can also place the sheet’s corners yourself (then those checks are yours to make), and you always see the toe and width lines on your photo, to move if they’re off, before you see a size.
We test it on 650 computer-rendered photos of feet of exactly known size, simulating three phone cameras, in different light, on different floors, in socks and bare feet, including photos made to fail. For the adult feet it measured, the median length error was 0.19 mm and 95% were within 0.63 mm. Real photos are messier than test ones, so each result shows a ± of at least 0.2 cm, and you can check the lines before you see your size.
Width
A width letter only means something at a given length, so there is no single width table. We use the brand charts that print a foot width for each fitting: New Balance, HOKA, Birkenstock. For a foot, we take the size its length gets on the brand’s chart, then the fitting whose width is nearest, with the line between two fittings halfway between their widths. Your category (narrow, regular, wide, extra wide) and US width letter come from New Balance’s chart, which prints a width for B, D, 2E, 4E (men’s US 6–16) and 2A, B, D, 2E (women’s US 5–13); for children, from Birkenstock’s kids chart (narrow and regular). Brands differ, so the foot width calculator also shows your fitting on each brand’s chart.
Converting a size you already know
A size covers a range of foot lengths, not one number. To convert, we take the range of feet your size fits and show every size in the other system that overlaps it. That’s why a conversion is sometimes two sizes (“US 9–9.5”): the other system’s steps don’t line up with yours.
The size systems
14 systems, each defined by its standard or its published table:
| System | Definition | Foot length | Sizes |
|---|---|---|---|
| Mondopoint | ISO 9407: size is foot length in millimetres; 5 mm steps for everyday footwear | foot_mm = size | 51 |
| Japan (JIS S 5037) | Mondopoint in centimetres: size is foot length in cm, 5 mm steps | foot_mm = size × 10 | 51 |
| South Korea (KS M 6681) | Mondopoint: size is foot length in mm, 5 mm steps | foot_mm = size | 51 |
| China (GB/T 3293.1-1998) | Mondopoint: size is foot length in mm, 5 mm steps | foot_mm = size | 51 |
| Mexico | Size relates foot length directly to centimetres | foot_mm = size × 10 | 47 |
| Europe (Paris point) | Paris points of 2/3 cm; approximately 1.5 × foot length (cm) + 2 | foot_mm = (size − 2) × 20 / 3 | 75 |
| Brazil | Paris-point scale offset by 2: Brazil = Europe − 2 | foot_mm = size × 20 / 3 | 35 |
| Argentina, Uruguay, Paraguay (Mercosur) | Paris-point scale offset by 1: Europe − 1 (Brazil + 1) | foot_mm = (size − 1) × 20 / 3 | 35 |
| United Kingdom (adult) | Barleycorns; size ≈ 3 × foot length (in) − 23 | foot_mm = (size + 23) / 3 × 25.4 | 31 |
| United Kingdom (children) | Children’s barleycorn scale; size ≈ 3 × foot length (in) − 10, from 0 to 13½ | foot_mm = (size + 10) / 3 × 25.4 | 28 |
| United States (men’s) | Men’s scale; size ≈ 3 × foot length (in) − 22 | foot_mm = (size + 22) / 3 × 25.4 | 35 |
| United States (women’s) | Common industry scale: women’s = men’s + 1½; size ≈ 3 × foot length (in) − 20.5 | foot_mm = (size + 20.5) / 3 × 25.4 | 28 |
| United States (children, C/K) | Children’s scale; size ≈ 3 × foot length (in) − 9¾, from 0 to 13½ (labelled C or K) | foot_mm = (size + 9.75) / 3 × 25.4 | 28 |
| United States (youth, Y/GS) | Youth/grade-school sizes share the men’s numbering (7Y = men’s 7) | foot_mm = (size + 22) / 3 × 25.4 | 13 |
Sources: en.wikipedia.org, senairs.org.br. Checked 2026-10-23.
Brand sizes
Brands don’t all follow the standard tables, so each brand’s sizes come from its own published chart: 51 brands, 254 charts, taken from each brand’s own site and linked from every brand row and on the brand chart pages.
- 145 of the charts give a foot length for each size. For those, your foot is matched to the brand’s own lengths.
- The others only print sizes (US, UK, EU). For those, we find your standard size and show the brand row that prints it. If no row matches exactly, the brand gets no row: we never estimate a brand size.
- Where a brand measures the shoe or insole rather than the foot, the chart says so and we keep that distinction.
Brand charts last checked 2026-10-22. Not affiliated with any brand.
How the numbers are checked
- Every row of data has a source and a date. A build with an overlap or a gap in a size table, or a row without its source, fails.
- Thousands of foot length → size cases taken from the brands’ own charts run as tests on every build.
- Every generated page’s answer and size table are recomputed from the data when the site is built; a live page that disagrees fails the build.
- Before pages are released, a script recomputes a sample with independent formulas and compares brand rows with the brands’ live charts; claims that don’t come from the data are checked against published sources.
What a size can’t tell you
Sizes are estimates to help you choose. Fit varies by brand, by model and by how a shoe is made, and some people prefer more room. If you’re between sizes or have wide feet, check the brand’s own advice. This isn’t medical advice.
Last reviewed 2026-10-23