Your shoe size starts with one number: the length of your foot in millimeters, from the back of the heel to the tip of your longest toe, measured while you stand. Every conversion on our size converter begins there. This guide shows how to take that number at home with paper, a pencil and a ruler, how to take a width measurement if you want one, and how the formulas turn a foot length into a US women’s, UK, EU or Japanese size.
What exactly gets measured
Sizing standards define foot length as the distance between two lines at right angles to the foot, one touching the most prominent part of the heel and one touching the most prominent toe. Two words in that definition matter.
Most prominent toe, not big toe. On many feet the second toe reaches farther than the big toe. The measurement goes to whichever toe sticks out most.
Right angles to the foot. The distance is measured straight along the foot, not diagonally from the heel to a toe that sits off to one side.
The Wikipedia summary of the standards adds the posture: the person stands barefoot, with weight spread evenly over both feet. It also notes that buyers of mass-produced shoes are advised to choose a size from the larger foot when the two differ.
Measuring length, step by step
You need a sheet of paper longer than your foot, tape, a pencil, a ruler or tape measure, and a second person if you can get one.
- Tape the paper to a hard floor with one short edge pressed against a wall.
- Stand barefoot on the paper with your heel touching the wall. Stand naturally, weight even on both feet.
- Have the helper hold the pencil straight up and down and mark the paper at the tip of your most prominent toe. A pencil held at an angle slides under the toe and adds a few millimeters.
- Step off. Measure from the wall edge of the paper to the mark, straight along the sheet, in millimeters if your ruler has them.
- Repeat with the other foot. Write both numbers down and use the longer one.
If you only have an inch ruler, read to the nearest sixteenth and multiply by 25.4 to get millimeters. A foot of 9 5/8 inches is 9.625 × 25.4 = 244.5 mm.
Measuring width, if you want it
Width does not change the size number in any of the systems below, but it explains why two pairs in the same size can feel different. The Mondopoint system labels shoes with both length and width in millimeters, for example 280/110. Width is defined as the horizontal distance across the ball of the foot, between lines touching the first and fifth metatarsophalangeal joints. Those are the knuckle-like joints at the base of the big toe and the little toe.
At home, stand on a fresh sheet, have the helper mark the outer edge of each of those two joints with the pencil held upright, and measure straight across between the marks.
U.S. shoes express width as letters instead. The Brannock Device, the measuring instrument Charles F. Brannock invented in 1925, measures foot length, arch length (heel to the ball of the foot) and width, and reads width on a scale from AAA to EEE. You see the same letters in recall notices: Naturalizer’s 2011 recall of Dare women’s dress shoes covered “sizes 5M to 10M, 11M, 7W to 9W,” M for medium and W for wide. That notice is on our Naturalizer Dare recall page.
Why you should not add room yourself
A shoe has to be longer inside than your foot. Wikipedia’s summary says the inner cavity “must typically be 15 mm longer than the foot,” and that the last, the foot-shaped form a shoe is built on, is usually about two sizes larger than the foot. The same article says ISO/TS 19407, the standard behind the formulas, derives sizes from foot length in millimeters “by adding an allowance of two shoe sizes.” Two UK sizes are 2/3 of an inch, about 17 mm.
The allowance is already built into the formulas below. Enter your bare foot length, not your foot plus the space you would like at the toe. Adding your own 15 mm on top would count the room twice and push you up about two sizes.
The formulas we use
With L as foot length in millimeters:
- UK = 3 × L ÷ 25.4 − 23
- US women’s (the FIA or “standard” scale) = UK + 2. Some brands use the “common” scale, UK + 2.5, which comes out half a size larger.
- EU (Paris points) = 0.15 × L + 2
- Japan (JIS S 5037) = foot length in centimeters, rounded to the nearest 0.5
If you measured in inches, the same formulas collapse to a shortcut: UK ≈ 3 × inches − 23 and US women’s ≈ 3 × inches − 21. The rounding step at the end is ours: we round to the nearest half size, which is how sizes are sold.
Three worked examples
A 240 mm foot (about 9.45 inches)
- UK: 3 × 240 ÷ 25.4 = 28.35, minus 23 = 5.35, so UK 5.5
- US women’s, standard scale: 5.35 + 2 = 7.35, so US 7.5. Common scale: 7.85, so US 8
- EU: 0.15 × 240 + 2 = 38.0, so EU 38
- Japan: 24.0 cm, so 24
A 9 3/4 inch foot (247.65 mm)
- UK: 3 × 9.75 − 23 = 6.25
- US women’s, standard scale: 8.25. Common scale: 8.75
- EU: 0.15 × 247.65 + 2 = 39.15, so EU 39
- Japan: 24.765 cm, so 25
This foot lands exactly between half sizes on the UK and US scales. That is a common result, and it is the case where the brand’s own chart, or trying both sizes, settles it.
Two feet that differ: 236 mm and 241 mm
- Left foot, 236 mm: UK 4.87 (UK 5), US 6.87 (US 7), EU 37.4 (EU 37.5), Japan 23.5
- Right foot, 241 mm: UK 5.46 (UK 5.5), US 7.46 (US 7.5), EU 38.15 (EU 38), Japan 24
A 5 mm gap moves every scale by half a size. Following the advice to size from the larger foot, this reader would start at US 7.5.
Mistakes that shift the result
- Measuring while seated. Sizing definitions assume you stand with your weight on both feet.
- Measuring to the big toe when the second toe is longer.
- A tilted pencil, which marks a spot under the toe instead of at its tip.
- Measuring diagonally to a toe that sits off-center, instead of straight along the foot.
- Rounding before converting. Convert the exact millimeter figure, then round the size.
How far to trust the conversion
The standard itself is modest about this. The catalogue entry for ISO 19407:2023, which replaced ISO/TS 19407:2015, says its tables “provide a guideline which can benefit the consumer.” It covers Mondopoint, European and UK sizing as well as China, Japan, Korea and the United States, all starting from foot length. Brands still cut lasts differently, so a measured foot length tells you where to start, not a guaranteed fit. Where the American, British and European scales part ways is covered in our sizes explainer, and data and methods lists the exact formulas behind the converter.
Sizes also matter when you check a recall. Notices often limit a recall to certain sizes, and imported styles sometimes list them in EU numbers: Birkenstock’s 2021 recall of Mogami kids’ sandals covered only “sizes 24-28,” about 15,200 pairs in the U.S. If you are checking a pair, the women’s footwear recalls list shows the size range of each notice.