Is there an exact number how much space we need in shoes? Different studies recommened that the optimal space for toes in shoes is 10-12 mm, but they also emphasise the important thing that space in front of the toes depend on the overall fit of the shoe too (toebox shape and width of the shoe).

Scientific studies

Ill-fitting shoes can cause many foot problems. Already Cheng and Perng [1] pointed out a really important fact in their article; you can eliminate many deformabilies just with choosing a proper footwear early enough.

According to Cheng and Perng [1] Hallux Valgus is just one deformability greatly influenced by shoe fit. They emphasied the important fact; shoes shouldn’t be too narrow or too short for your feet, which may squash your toes together and lead to this deformability.

There were different studies performed on how insufficient length of the shoe affect the hallux angle. Larger studies have been conducted on children from Austria, Finland and Japan and I will mention these here.

Klein et al. [2] published a study where they examined the relationship between insufficient length of footwear and the hallux angle in pre-school children. The study was performed in Austria on 858 pre-school children. The results were extremely worrying.

Number of children in the 5 categories of hallux valgus angles. (source: Klein et al. [2])

Only 23.9% of the children feet had perfectly straight position of a great toe. Only 22.8% wore properly fitting outdoor shoe and only 9.4% properly fitting indoor shoe. Properly fitting shoe was considered to be at least 10 mm (optimally 12 mm) longer than the foot. Klein et al. [3] proven a clear relationship; the shorter the shoe was, the greater the hallux valgus angles was.

Another study was performed by Kinz et al. [3] where their examined children feet and shoes from Finland. They investigated whether children are wearing properly fitting shoes. They came to the conclusion that the shoes are not labelled properly and is recommend to measure the length of the child’s feet and also the inside length of the shoe to ensure 10-12 mm space required in them.

How to measure shoes and feet you can find in my post here.

In most recent study from dr. Kinz et al. [4] they examined the effect of too-short shoes on the hallux angle in preschool-aged children in Japan. The study was made on 620 kids and the results were worrying. Only 12.3% had straight positions of the big toe and 75.5% wore outdoor shoes of insufficient length (84.6% for indoor shoes). They confirmed again everything what was shown in previous studies. The shorter the shoe, the greater the hallux angle.

Those articles you can download here. If you understand German you can listen to an interview done by Alex from Barfuss im Pott with dr. Kinz here.

These stuides were the basis on which Plus12 measure was developed. I would also point out that these researches were done on children who wore conventional shoes and not barefoot. However, it is in the future interest to do research on children who have worn barefoot shoes all their lives.

Another important study was published in 2016 by Barisch-Fritz et. al. [5]. The study investigated toe allowance for developing feet. They investigated 2554 children aged 6-16 years during standing and walking. Toe allowance was determined with taking into account foot extension (difference between static and dynamic weight-bearing), walking advance (movement of most anterior points of toes) and growth rate (semi-annual foot growth).

They came to the conclusion that toe allowance is influenced by gender and foot length. The 90th percentile of toe allowance from their study was 9.8 mm for female and 11.5 mm for male. This number already included growth rate which was the main cause for differences by gender. The 90th percentile of semi-annual growth rate was between 3.1 and 5.6 mm (it depended on the age and gender).

Those measurements in the study were made on kids being barefoot. They emphasized here one important thing; the amount of toe allowance in shoes depends on the overall fit of the shoes.

What does that mean?

According to dr. Kinz, 12 mm is the optimal space inside the shoe (10 mm lower limit) and this is the space I always try to choose. When I’m in between sizes I allow less space (cca. 3 mm) if:

  • I wear those shoes sockless
  • toebox shape match my foot shape extremely well
  • shoes have very generous toebox with a lot of space for big toe
  • shoes are perfectly secured around the heel, so no foot sliding happens
  • the shoes have enough space above the toes
  • my heel fit in the heel part well, so no extra space is lost there
  • shoes are made from a material that feel like socks on feet
  • I wear sandals (not closed-toe) – in that case I choose 7-10 mm to prevent tripping

We cannot therefore say in general that e.g. 8 mm is a lower limit when you should change children’s shoes or that this is the lower limit for adult shoes.

Much also depends on the width and shape of the shoe and how well the shoe mimics our foot shape, how much our foot stretches while walking (it would be necessary to analyze the foot), if we wear socks in the shoe, fixing the foot in the shoe, fit in the heel part, etc.

It should also be noted that usually the inner lengths of the shoes in the size tables are measured from the middle part of the heel to the point between the big toe and the second toe (which is usually the longest part of the shoe), so the space you have for your toes is usually slightly smaller than that value. How small it is depends on the shape of the shoe (how strong the slope is) and the shape of the foot.

Due to the rounding of the shoe, the actual space we have in front of each toe depends on the location of the toes and the internal length of the shoe at that location.

With a shoe, it is simply very difficult to ideally mimic the shape of the foot and the extension of the foot during barefoot walking, and with 10-12 mm of extra space we allow taking all factors into account.

When to choose more than 12 mm space inside the shoe? 

  • in winter boots which you wear with thicker socks
  • when you wear shoes with insoles, which can take away some space
  • when you are in between sizes
  • if you need more space in toebox area (more width or toebox shape is not ideal) and you can comfortably walk with more space
  • for kids – their feet are still growing

Remember, always measure your foot well (you have a full guide here).

Research conclusions

There are clear conclusions from all the researches. There should enough in front of your toes to avoid damage to your feet. While walking your feet moves and you need that space for rolling your foot. If there is not enough space there, the hallux angle will increase.

Where is the limit now?

Dr. Kinz recommends 17 mm too big and under 10 mm too small, optimal 12 mm. But there is no researches available how to big influence on your feet and gait.

Take in mind that 12 mm is valid only for closed shoes. For winter shoes where you wear thick socks you can add few mm more too. For open sandals where your toes are free it is recommended to have 7-10 mm extra space in them.

What about kids whose feet constantly grow?

Buy shoes with up 15 mm space and replace them at 10 mm. And check their foot length regulary.


A lot of times we want to show how much space we :have in the shoe with our index finger. This can serve you only as a quick guide.

HINT: the average with of index toe is approximate 15 mm, thumb 17 mm and pinky finger around 12 mm. You need 12 mm in the shoe.

An interview with Dr. Wieland Kinz

Here I’m sharing with you a short interview which Sonja from Instagram profile mini.and.mum had with Dr. Wieland Kinz, which was one of the main actors in the studies mentioned above.

Does the 12 mm space in front of the toes applies for each foot and also for barefoot shoes and for conventional ones?

Let’s start where there a reseach about less space started: In 2009, we were able to show that – starting from 10 mm space – that with every millimetre less space the risk of developing hallux valgus increases significantly (see Klein [2]).

This was also confirmed in our last study in Japan (we have already submitted the publication to a journal). This means very simply: regardless of what footwear your feet are in, you need this freedom in front of your toes. But only if you want to avoid foot damage😊

Children’s feet have softer structures and therefore need a relatively (not absolutely) more rolling space.

Exactly. We like to compare this – plastically😊 – with a piece of soft and hard rubber. If you press the soft rubber, it spreads more than the hard one. It should be something like this for us with children’s feet. Due to the still very soft structures, there are some indications that the space required for small feet is relatively larger than for large feet.

Studies show significantly increased misalignment of the big toes with less than 10 mm available space.

Yes, see above our study from 2009. This was confirmed again in our Japan study. In our view, the results of this study are extremely interesting. In Japan there is a “barefoot policy” in almost all kindergartens. So children have to be barefoot in kindergarten.

And we were lucky to be able to measure in our kindergartens with “barefoot-policy” as well. We measured kids who wear slippers in kindergarten and we measured kids who always were barefoot in kindergarten.

It was not only confirmed that shoes that are too short have an effect on the Hallux angle, but also the unexpectedly large (positive) influence of walking barefoot was shown.

Example: Those children who wore shoes, that matched the best regarding the length they need, had the smallest big toe angles. But the absolute best were the children who were barefoot. Based on our calculations, walking barefoot must have a multi-dimensional preventive function that even goes as far as to compensate for misalignment of the big toe.

Studies also show that feet move more in flexible shoes than in rigid shoes and according to that the space required in barefoot shoes tends to be even larger than in conventional shoes.

Yes, that’s how it looks.

In the case of non-anatomically shaped toe boxes, you should measure with the plus12 measuring device as the foot would also stand in the shoe. This means even larger addition to total shoe length than 12 mm if the big toe area is rounded and the longest point in the shoe is elsewhere (like in the middle of the shoe)?

Yes, motto: there should be at least 12 mm space in front of the longest toe. No matter what the shoe looks like.

Does all information here also applies to adult feet, like here in where 10-20 mm is mentioned?

Yes, I have described this before. We also assume a minimum space of 10 mm in the statistical calculations (and mention the optimum space of 12 mm) and for the time being we describe shoes with more than 17 mm space as too long.

However, this is where it becomes scientifically difficult: With “too long”, the question arises: what does it matter and how does it work? And of course, the whole thing in the background: How good is the foot in too long shoe e.g. how the shoe hold the foot at the ball of the foot and if the foot does not slide back and forth while walking in too long shoe.

Note: We have already carried out tests on marathon runners and found that they had up to 20 mm of space.

Do you happen to know of any studies that talk about the necessary width?

No, not until today. From a scientific point of view, there is still no knowledge of how wide-fitting shoes should be. And then the question immediately arises: width – but where? At the ball of the foot, it is also important that the foot does not slide back and forth in the shoe, but we do not know that either: a little narrower than the foot, the same width, a bit wider?

Anatomically we can hardly damage anything in that area. It looks quite different in the toebox area: it seems logical that the width would be very important. According to that, someone would have to measure the width of the toes and the width of the exact place where the toes are located in the shoe.

Exciting news: one of the reasons why we were taken aback by conventional socks was because the toe area seemed very wrong to us. And then we took X-rays of barefoot feet and feet in traditional socks. See the photo below. And that’s how the idea of ​​plus12socks came about …

We compared the toe position in regular socks and plus12socks. It is certainly similar in shoes too.

Position of the toes when being barefoot (left) and in normal socks (right)


I would like to thank my friend Sonja and Dr. Kinz that they allowed me to post an interview on my blog.

[1] Cheng, F.T., Perng, D.B. A systematic approach for developing a foot size information system for shoe last design. Int J Ind Ergon., 25, 171-185 (1999). 10.1016/S0169-8141(98)00098-5.

[2] Klein, C., Groll-Knapp, E., Kundi, M. Increased hallux angle in children and its association with insufficient length of footwear: A community based cross-sectional study. BMC Musculoskelet Disord 10, 159 (2009).

[3] Kinz, W., Groll-Knapp, E. & Klein, C. Kinder in zu kurzen Schuhen. Paediatr. Paedolog. Austria 50, 106–109 (2015).

[4] Kinz, W., Groll-Knapp, E. and Kundi M. Hallux valgus in pre-school-aged children: the effects of too-short shoes on the hallux angle and the effects of going barefoot on podiatric health, Footwear Science. 13:1, 29-42 (2021). DOI: 10.1080/19424280.2020.1853826

[5] Barisch-Fritz, B., Plank, C. and Grau, S. Evaluation of the rule-of-thumb: calculation of the toe allowance for developing feet. Footwear Science. 1-9 (2016). 10.1080/19424280.2016.1144654.


The shoe will fit you well if:

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