Stand to Measure: Find Your True Shoe Size in Millimetres

by YDA UK

Measure both feet while standing and use the larger foot’s millimetre measurements with the retailer’s size chart. Do this at the end of the day, when feet have naturally swollen from hours on your feet, since a morning measurement can undersell your true size. Record length and width separately: the two numbers together tell you far more than a single shoe size ever could.

TL;DR:

  • Measuring feet at the end of the day captures natural swelling, resulting in more accurate shoe fit than morning measurements.
  • Use a standing, weight-bearing method with a ruler in millimetres to get reliable length and width measurements, especially for atypical feet.
  • Shoes should fit with about a thumb’s width of space beyond the longest toe and 10 to 12 millimetres of extra length for comfort.
  • Digital tools and phone apps offer convenient millimetre measurements, but professional fitting is recommended for foot conditions or persistent fit issues.
  • Regional sizing systems, brand differences, and shoe lasts mean always check retailer-specific size charts and prioritize fit over size labels.
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Table of Contents

Step-by-step home measurement using paper, a pencil and a ruler

You need almost nothing for this: a sheet of A4 paper or card, a pen or pencil, a hard-backed ruler marked in millimetres, and a strip of tape to stop the paper sliding.

  1. Stand on the paper, barefoot or in thin socks, with your heel touching a wall.
  2. Hold the pen vertically and mark the paper at the tip of your longest toe (this is not always the big toe).
  3. Step off and measure the straight-line distance from the wall edge to the mark, in millimetres.
  4. Repeat the whole process for the other foot, since most people have one foot slightly larger than the other.
  5. Mark the widest points of the forefoot (the first and fifth metatarsal heads) and measure that width in millimetres too.

Keep the pen upright when marking. A slanted pen or an inch-only ruler introduces small errors that add up once you convert to a size.

Once you have both numbers, round to the nearest millimetre, or to the nearest 5 mm if the chart you’re using groups sizes that way. If your length falls between two sizes, take the larger one, then check the retailer’s guidance on width, since some brands run narrow through the toe box regardless of length.

  • Fit check: with the shoe on and laced, you should be able to fit roughly a thumb’s width between your longest toe and the front of the shoe.
  • General guidance suggests leaving 10 to 12 millimetres of extra length beyond your measured foot, though this varies with shoe style.

Pro Tip: Trace both feet on the same sheet so you can compare them side by side before you commit to a size.

Tools and technology: phone apps, photo methods and in-store measurers

Phone apps that ask you to stand on a reference sheet or place a card of known size next to your foot can return length and width in millimetres without any manual tracing. They’re convenient, but they inherit the accuracy of whatever photo angle and lighting you give them.

Handheld 3D scanning and pedobarography (pressure-mapping while standing) tend to give reliable distance measurements in clinical and lab settings, but these methods are not interchangeable with simple photo-based apps, and results can diverge, particularly for width and angular measurements. A phone photo or manual trace is generally close enough for ordinary shoe shopping, but it will not match a clinical scan exactly.

When choosing a digital method, look for:

  • A tool that asks you to stand for the measurement rather than sit or lie down.
  • Output given in millimetres, not just a converted shoe size.
  • The option to save measurements for both feet separately.

If you have a medical condition affecting your feet, such as diabetes, or you’ve had ongoing fit problems that home measurement hasn’t solved, a professional fitting or podiatric assessment is worth the extra step. Weight-bearing measurement consistently outperforms seated or lying measurement for predicting real-world fit, since foot dimensions change under load.

Converting measurements to sizes and common pitfalls to avoid

Millimetre-based measurement isn’t arbitrary. It’s the basis of ISO 9407, the mondopoint sizing system, which defines shoe size from weight-bearing foot length and linear width. UK, EU and US sizing systems all derive from length, but they use different increments and starting points, which is why a size that fits in one system rarely lines up neatly with another.

Brand differences compound this. Lasts (the mould a shoe is built around), grading tables and limited width ranges mean two shoes labelled the same size can fit noticeably differently. Research analysing 1.2 million foot scans found wide variation in foot shapes across regions, and concluded that grading tables and lasts haven’t kept pace with that diversity, which is a large part of why a single nominal size fits inconsistently between brands.

Measurement source What it captures Why it matters
ISO 9407 / mondopoint Weight-bearing foot length and linear width in millimetres Basis for translating a measurement into a size
UK/EU/US charts Length converted to a regional size scale Systems differ in increments, so sizes don’t map one-to-one
Brand-specific lasts Shape and volume of the shoe mould Explains why the same labelled size fits differently across brands

A few rules keep you out of trouble:

  • Always check the specific retailer’s size chart rather than assuming a size carries across brands.
  • Measure both length and width, and size to your larger foot.
  • If you’re between sizes, size up and check whether the brand offers width options.
  • When still unsure, favour a style with adjustable fastening, such as laces or straps, which can absorb small sizing errors.

Measuring children’s feet and how often you should re-check

Children’s feet grow quickly and often unevenly, which is why the same standing, heel-to-toe method needs repeating far more often than for adults. Guidance drawn from research on children’s footwear measurement suggests re-measuring infants roughly every 6 weeks, moving to about every 3 months for toddlers, and every 6 months for older children, since surveys found many children wearing shoes that no longer fit.

  1. Stand your child against a wall on the paper, steadying them if needed, and mark the longest toe the same way as for an adult.
  2. Measure both feet, since one is often slightly larger.
  3. Label and date the tracing, or photograph it, so you can compare it directly at the next check.

Pro Tip: A strip of card cut to the measured length makes a quick, reusable “go/no-go” gauge for checking growth between full re-measurements.

If a child consistently favours one foot, complains of foot pain, or you notice an unusual walking pattern, that’s worth raising with a health professional rather than solving with sizing alone.

Measuring children's feet and how often you should re-check — overview diagram

Tips for trying shoes on and assessing fit beyond size measurement

A millimetre measurement gets you to the right size on paper, but the fit test happens with the shoe on your foot. Try shoes on both feet, standing rather than sitting, since your foot spreads and lengthens slightly under weight. Walk a few steps on a hard floor, not just carpet, to feel how the sole flexes and whether your heel lifts.

Check the width across the ball of the foot first. A shoe that’s the right length but pinches at the widest point will never feel comfortable, however good the length measurement was. Wiggle your toes: they should move freely without hitting the front of the shoe, and there should be roughly a thumb’s width of space beyond your longest toe.

Three checks for comfortable shoe fit

Pay attention to how the shoe sits around your instep and heel. A gaping heel or a tongue that presses down hard on the top of your foot points to the wrong last shape for your foot, even if the labelled size matches your measurement. If you have a noticeably high or low arch, or feet that are wider or narrower than average, expect to need to try more than one brand before finding a shape that suits you.

Bring the socks you’d actually wear with the shoes, and if you know your feet swell later in the day, try shoes on in the afternoon or evening rather than first thing in the morning.

Brand perspective: why accurate fit matters

Getting the size right is only half the job. Some footwear brands build shoes around technology designed to stabilise each step and support foot health, which only works if the shoe fits properly in the first place. Once you’ve measured, our size guides and YDA Technology pages can help you choose footwear that matches both your measurements and how your foot actually moves.

— Panagiotis

Sources

This guide draws on ISO 9407, weight-bearing foot deformation research, and large-scale foot scan analysis. For printable charts, see our home measurement guide.

FAQ

How can I figure out my shoe size?

Stand on a piece of paper, mark your heel and longest toe, then measure the distance in millimetres for both feet. Use the larger foot’s measurement against the retailer’s own size chart, since sizes vary between brands.

What is 40 in shoe size?

A size 40 typically falls in the EU sizing system and corresponds to a specific foot length in millimetres under ISO 9407. Because lasts and grading differ by brand, it’s best to check the exact millimetre range against the specific retailer’s chart rather than assuming it matches another region’s size 40.

What shoe size is 7?

A shoe size means different things depending on whether it’s a UK, US or EU size, since each system uses its own length increments. Measure your foot in millimetres and check the specific retailer’s conversion chart to find the size that actually fits your foot.

How do I check my UK foot size?

Measure your foot length in millimetres from heel to longest toe while standing, then compare that figure against a UK size chart, which converts length to the UK’s own size scale. UK sizing differs from EU and US systems in its increments, so a millimetre measurement is the most reliable starting point.

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