How do you choose the right shoe size?

In more than 15 years of working with barefoot shoes and helping people find the right size every day, I’ve noticed a very familiar pattern: parents often buy shoes that are too big for their children, while choosing shoes that are too small for themselves. Not everyone, of course, and not every time. But it happens often enough that it stopped surprising me long ago.

That’s why so much of my conversation with a customer, especially on their first visit, isn’t really about which model to choose. First, we need to find the right size. And the problem is usually the exact opposite for children and adults: parents often want far too much growing room in their children’s shoes, while adults have become used to shoes with practically no room for their feet at all.

For children: too big “so they’ll last longer”

I understand the reasoning when it comes to children. Feet grow, shoes cost money, and naturally you’d rather not have to buy another pair just a couple of months later. Children’s shoes really do need growing room, but very often parents allow too much of it.

What we regularly see in practice is a shoe where the extra room is no longer just extra room — it’s a couple of sizes too much. Parents think they’re saving money because the shoes will last longer, but sometimes the opposite turns out to be true.

When a shoe is much too big, the child’s foot isn’t positioned where the shoe was designed to accommodate it. The sole bends in the wrong place, the toe catches on the ground more often, the shoe gets dragged along the surface instead of moving naturally with the foot, and different parts of its construction take stress they weren’t meant to take. As a result, the shoe may lose its shape, wear through at the toe or start tearing in places where a correctly sized shoe might have lasted much longer.

You can see this particularly clearly with thin barefoot rubber boots. If a boot is far too big for a child, they effectively drag it along the ground, repeatedly rubbing the heel against an abrasive surface. A month or two later, a parent comes back and says, “But we only just bought these, and there’s already a hole!” I’ve seen more extreme examples too, where boots were damaged this way in just a few weeks. After so many years, we’ve become pretty good at recognising when shoes simply haven’t been the right size.

So when someone tells me, “I want a bigger size so they’ll last longer,” my answer is often that it might work out exactly the other way around: shoes that are too big may wear out sooner.

But the child matters even more to me than how quickly the shoes wear out. I can see when shoes are too big and a child starts adjusting their way of walking to cope with them. If there’s far too much space at the front, the child has to lift their feet higher so the toes of the shoes don’t catch on the ground. Sometimes they turn their feet outwards and walk a little like Charlie Chaplin, because that makes it easier to move those long shoes forward. In other cases, you might barely notice anything from the outside, but inside the shoe the child starts curling their toes to keep it on. Even when a shoe is secured around the ankle with Velcro or laces, the foot may have so much room inside that the child instinctively tries to stabilise it by tensing the front of the foot.

Sometimes a parent then notices that the child’s foot rolls inwards or their walking becomes less stable, and concludes that the shoe isn’t providing enough support — perhaps they need a firmer heel counter, arch support or something else. If this is their first experience with barefoot shoes, the verdict can be quite definite: “Barefoot shoes aren’t suitable for my child.” But perhaps it’s simply the size that isn’t suitable.

I’m not claiming that an oversized shoe will automatically cause overpronation or a particular foot deformity. What I do see regularly is children compensating and changing the way they walk when their shoes are too big. If we choose barefoot shoes to interfere as little as possible with a child’s development and natural movement, it makes little sense to buy a well-designed, anatomically shaped shoe and then choose it so large that the child has to change their gait just to walk in it.

How much growing room does a child need?

We generally recommend approximately 5–7% of the foot’s length. I don’t like using one fixed number, such as 12 mm for every child, although that figure is often presented as a universal allowance in the barefoot shoe world. Some popular measuring tools even add it automatically.

If a child’s foot is 10 cm long, an extra 12 mm is already more than 10% of the entire foot length — a huge amount for such a small foot. Think of a woman with a foot around 23–24 cm long and imagine her wearing shoes with more than 2 cm of extra space, especially if walking were still new to her and she were only just taking her first steps. On the other hand, for a child or teenager with a 22 cm foot, those same 12 mm are perfectly reasonable. That’s exactly why we look at growing room proportionally: the allowance increases as the foot grows, rather than adding the same number of millimetres for every child.

Adults have exactly the opposite problem

With adults, especially women, I often see a completely different situation. An adult usually walks into the shop and immediately tells me their shoe size. Yet sometimes, even as they come through the door, I can see that their shoes look too small in proportion to their height. The human body tends to have certain proportions, and in my experience it’s relatively unusual for someone’s foot length to be completely out of proportion with their height and the length of their arms and legs.

Still, I never argue. I let people see for themselves whether that familiar number actually matches their feet. If someone says size 39, we start with 39. I bring the shoe over, but before they put it on, I take out the insole and ask them to stand on it. Very often we can both see immediately that it’s too small. The customer doesn’t even try the shoe on — they ask me to bring the next size instead. 

If the foot spills over the sides of the insole, the toes reach right to its edge and there’s practically no space at the front, I don’t need to explain much. We try a 40, sometimes even a 41. It’s not unusual for a woman who has bought size 39 all her life to leave my shop with a size 41 and a very surprised expression. If I had to put a number on what I see, I’d say that before these conversations, people have often spent their lives wearing shoes around one and a half to two sizes too small.

Some women don’t quite believe me the first time and buy something halfway between the size they originally asked for and the one I recommended. But I still think that’s a step towards giving their feet more freedom. And quite often, when they come back for their next pair, they admit I was right and ask for a size bigger themselves. They’ve discovered how good comfortable shoes can feel — and now they want even more comfort :)

Of course, for women this is partly psychological. Somewhere in society, the idea that small feet are beautiful feet is still deeply ingrained. When a woman comes into the shop and immediately adds, “I have small feet,” I sometimes reply — if I feel she’ll take the joke in the spirit intended: “You don’t have small feet. You have small shoes.”

Did you know that, for many people, foot length is roughly the same as the distance from the wrist to the inside of the elbow? Perhaps that’s part of why I can sometimes spot shoes that are too small before a customer has even taken them off.

And to complicate matters further, there isn’t one universal standard for shoe sizes. European shoe sizing historically comes from a measurement of the shoe last. But every manufacturer designs its own lasts, so the shapes vary — and so do the internal lengths and widths of the shoes. There’s a funny but rather accurate joke about this online (watch it if you need a laugh!). In reality, the size number tells us surprisingly little. It’s just a rough starting point for the conversation. 

A very simple test you can do at home

What we do in the shop to check whether shoes fit is actually very easy to try at home. Take the insole out of your shoe and stand on it. 

The first thing I look at is length. For an adult, the shoe should be approximately one centimetre longer than the foot. That’s roughly how much space you should see on the insole in front of your toes when your heel is positioned where the insole begins to curve upwards at the back (or right at the back edge if the insole is completely flat). Some barefoot shoe manufacturers recommend 8–10 mm of extra space, while others insist on at least 12 mm. But the general idea is the same: around one centimetre of room in front of the toes.

For adults, that space obviously isn’t there to allow the foot to grow. It’s there to allow it to move. Your foot moves inside the shoe as you walk. When you take a step and transfer your weight towards the front of your foot, your foot lengthens under load and moves forward. Remember that right now you’re standing on the insole, but we don’t buy shoes just to stand still. As you walk, your toes move forwards again and again, and without enough room this can have consequences: toes get bent, nails are pressed against the shoe and may sometimes become ingrown, one toe starts trying to find space above another, and calluses and other problems may develop.

The second thing I look at is width. The entire foot should fit on the insole. Ideally, I even like to see a millimetre or two of space along the sides. If your foot already extends a millimetre or two beyond the edge of the insole while you’re standing still, it’s a strong sign that there won’t be enough room inside the shoe when you move. Your toes may be squeezed together instead of being able to move freely. Try shifting your weight towards the front of the foot, as though taking a step. You can clearly see how the foot spreads. If it already fills the insole right to the edges while standing, there’s nowhere left for the toes to go when you move. This test can be especially revealing with conventional shoes: the narrow, tapered toe box is reflected in the shape of the insole, making it very easy to see just how little space there is. It’s also a good illustration of why barefoot shoes are becoming increasingly popular.

After all, it’s the anatomical shape and wide toe box that allow your feet to feel free rather than squeezed throughout the day. That’s why it makes no sense to choose barefoot shoes for their foot-shaped design and then buy them too small. Yes, they may still be better than narrow conventional shoes that are also too small, but we’ve taken away much of the very benefit that made us choose barefoot shoes in the first place.

How to measure your feet at home

If you’re coming to our shop to buy shoes, it isn’t essential to know your own or your child’s exact foot length in millimetres. We’ll measure it with a special device in the shop anyway and work out the right size together. Still, knowing your child’s approximate foot length is useful: it can spare them some unnecessary fuss during the fitting, and it helps you keep track of whether their current shoes are becoming too small. 

But if you’re buying shoes online, measuring your feet properly at home is essential. The easiest method is to stand with your full weight on a sheet of white paper. You don’t necessarily need to trace the entire foot — you can simply mark the furthest point of the heel and the longest toe. If you also want to measure width, mark the widest points of the foot. I recommend tracing the whole foot when it’s difficult to tell exactly where those widest points are.

Just make sure you hold the pencil vertically against the paper. Don’t angle it underneath the foot or draw a line outside its actual outline, or the measurements won’t be accurate. Once you’ve marked the points, draw straight lines and use an ordinary rigid ruler to measure between the perpendicular guide lines, as shown in the illustration. You can then use these basic measurements to work out how much extra room you need. One common mistake is using a soft tailor’s measuring tape to measure the drawing. Those tapes can stretch, and a well-used one can sometimes be off by as much as a centimetre. Don’t simply hold a ruler against the foot and guess, either, or bend a flexible tape around a child’s foot. Neither method gives you a reliably accurate measurement, and you may end up having to return the shoes you ordered online. 

Always measure both feet, because for many people they aren’t exactly the same size. Choose shoes based on the larger foot. You now have the actual length and width of the foot — but don’t confuse those measurements with the internal length your shoes need to have.

For example, if a child’s foot is 15 cm long, we add approximately 5–7%, which means looking for a shoe with an internal length of at least 15.8 cm but no more than 16.1 cm in this example. If an adult’s foot is 25 cm long, we look for a shoe with approximately 25.8–26.2 cm of usable internal length. Then we can compare those measurements with the size chart for the particular brand.

Once you’ve done this homework properly, finding the right shoe size online isn’t all that complicated. Of course, there are still other things to consider: foot width, instep height, the shape of the particular model and more. So whenever possible, it’s better to come and try shoes on in person. Even different models from the same manufacturer can fit differently, not to mention how different brands feel on your feet.

The most important thing about shoes is that they fit

We can talk endlessly about the benefits of barefoot shoes — wide toe boxes, zero drop, flexible soles and everything else. But none of that matters very much if the shoes themselves don’t fit you. Of course, you have to like the way they look, too. I wouldn’t buy shoes I thought were hideous just because they were anatomically perfect. If you don’t like your shoes, you simply won’t wear them. But first and foremost, they have to fit.

Don’t buy shoes so big for a child that they might last two winters. And don’t buy shoes too small for yourself just because you’ve always worn size 39 and the thought of wearing a 41 somehow bothers you. Find shoes that allow your feet to sit naturally and move comfortably.

For me, a good shoe is one I forget about during the day. When I get home, my first thought as I walk through the front door isn’t, “Finally, I can take these shoes off!” I can cuddle the dogs, unpack the shopping, do a few more things for another ten minutes — and only then take my shoes off.

I don’t wear shoes around the house because I’m not used to it, but I easily could. People in our shop often put on a pair of barefoot shoes or boots and say, “Oh, they feel like slippers!” And yes — that’s exactly how I think shoes should feel. All shoes, not just slippers. Shoes shouldn’t spend the whole day pinching, rubbing, restricting you or constantly reminding you that you’re wearing them. Your feet should feel almost as comfortable as they do barefoot or in socks.

And next time, we can talk about one more thing that can very effectively spoil all of this: socks.