What shoe size is 38 2/3, and how do you get the right size when buying?

Size 38 2/3 is, in practice, equivalent to a European 38.5 in most brands that use fractional sizing, especially Adidas. That fraction is not arbitrary: it responds to a finer sizing system that makes it possible to better adjust the length of the foot, something crucial in sports, urban, or technical footwear.

The usual equivalence places that number between 38 and 39, with an approximate foot length close to 24 centimeters, although the final fit depends on the last, the model, and the intended use. In running shoes, for example, a minimal margin can completely change the feeling of comfort while running.

What size 38 2/3 really means

Fractional numbering was created to fine-tune the fit between whole sizes. Instead of jumping from a 38 to a 39 with no middle ground, some brands introduced intermediate steps that reduce the margin for error. Adidas is the best-known reference in this system, and its 38 2/3 is usually read as a long 38.5.

That nuance matters because the foot does not behave like a fixed storefront measurement. It expands over the course of the day, changes with the type of sock, with activity, and with heat. A pair that seems right at home may feel short when running, pinch at the instep, or leave the heel too loose after several kilometers.

The key is not only the numerical equivalence, but how the shoe behaves on the foot. The same size may feel roomier in a shoe with a wide last and tighter in a narrow model. That is why translating 38 2/3 to 38.5 helps, but does not by itself solve the purchase.

Approximate equivalences in the European system

In the EU system, 38 2/3 usually sits around a 38.5. It is a useful equivalence for orientation, although it does not always appear in exactly the same way in all charts. Some stores show it as 38 2/3, others as 38 2/3 EU, and others directly as 38.5. The practical result is the same: an intermediate point between two classic sizes.

In centimeters, that size is usually associated with a foot of around 24 cm, with small variations depending on the manufacturer. That figure should not be taken as a rigid truth, because the useful measure is not only foot length, but also forefoot width, instep height, and the overall shape of the arch.

Comparison with other numbering systems can be misleading. In the UK or the US, the equivalence changes completely and should not be converted casually. The most reliable approach is still to consult each brand’s specific chart, because a 38 2/3 in Adidas does not always translate the same way in other brands that use standard European sizing.

Why an intermediate size can make all the difference

In sports footwear, half a size can be the difference between comfort and rubbing. In a walking shoe, that margin may go unnoticed. But in a running shoe, a hiking boot, or a mountain model, the foot moves forward on descents, swells with effort, and needs a minimal reserve so it does not hit the toe box.

That reserve does not mean buying bigger by default. Too much room causes internal slipping, loss of precision, and heel blisters. The ideal fit leaves enough space to move the toes, but keeps the foot held securely like a firm hand, not like a rigid clamp or a borrowed shoe.

The intermediate size is especially useful for people who are torn between two adjacent sizes. It also works well when the model runs small or when the foot has a slight asymmetry. In sport, that small variation is felt more in the dynamics of the step than in static use.

How to measure your foot properly before buying

Measuring the foot in centimeters remains the most sensible method. Simply place it on a sheet of paper, mark the heel and the longest toe, and measure the maximum distance. It is advisable to do this with both feet, because it is not uncommon for one to be slightly larger than the other. In that case, always go by the longer foot.

The measurement should be taken at the end of the day or after walking for a while. Feet tend to swell somewhat as the hours pass, and that difference, though it may seem small, helps avoid shoes that are too tight. It is also a good idea to measure wearing the type of sock that will actually be used, especially for running, hiking, or mountain activities.

The golden rule is to leave a small functional margin. In general-purpose footwear, that margin can be minimal; in running shoes or technical boots, it is usually wiser to allow a few extra millimeters in front of the toes. What matters is that the foot is neither compressed nor sliding around inside the shoe.

What changes depending on the brand and the last

Two pairs with the same size can feel very different. Length is only part of the issue. The last, which is the shoe’s internal shape, determines whether the fit will be narrower, higher over the instep, or wider in the forefoot area. That is why a 38 2/3 may be perfect in one brand and tight in another.

Adidas is the brand that has most popularized fractional sizes, but even within its catalog there are differences between ranges. A lightweight running shoe does not behave the same as a lifestyle shoe or a training boot. The fabric, tongue, cushioning, and heel stiffness all alter the final perception.

The feeling of the correct size depends not only on the number, but on the whole package. There are models that wrap the foot precisely and others that need more room so as not to punish the forefoot. That is why, when buying online, a good size guide is worth more than the memory of an old size, because fit varies even within the same brand.

What to do if you are torn between 38 and 38 2/3

When the doubt is between two neighboring sizes, intended use is the deciding factor. For walking or everyday wear, the more snug option may work if it does not pinch. For running, training, or spending many hours on your feet, it is usually safer to choose the intermediate point or the one that leaves a slight amount of room in front.

It is also worth considering foot shape. A narrow foot may tolerate a slightly longer size better, as long as the heel does not slip. A wide foot, on the other hand, benefits from more lateral space, even if the length seems right. The most common mistake is focusing only on length and forgetting width.

The type of activity matters more than aesthetics. A casual shoe can allow for a more exact fit. In contrast, in running or mountain activities, a size that seems perfect while standing still may end up feeling too short in motion. The body changes as it moves forward, and the footwear must adapt to that change without fighting against it.

Size 38 2/3 in running, mountain activities, and everyday use

In running, an intermediate size is often an ally. During the stride, the foot moves forward by millimeters and the repeated impact multiplies any fitting error. A reasonable amount of space in the toe box helps prevent black toenails, toe pressure, and a feeling of restriction on long runs.

In mountain activities, the demands are even more delicate. Climbs strain the instep and descents push the foot forward. There, a size that is too tight becomes a silent trap. The right balance is like a well-pitched tent: firm, with no unnecessary tension, but with nothing loose where it should not be.

In urban or everyday use, the size may feel different because of cushioning and material. Soft or heavily padded shoes can give the impression of more interior space. On the other hand, a rigid or narrow-cut design can make the same number feel shorter. The foot’s experience always has the final word.

Common mistakes when interpreting this number

One of the most common mistakes is converting 38 2/3 as if it were exactly 38 or 39. That reading erases the meaning of the fraction and can lead to an incorrect fit. The intermediate step exists precisely to avoid that abrupt jump, so it is worth respecting its true equivalence in the brand’s chart.

Another common error is thinking that all European sizes behave the same. They do not. Some manufacturers have longer lasts, others narrower ones, and some add a feeling of compression over the instep. Two pairs marked with the same number may require different choices.

The effect of real use is also often underestimated. A shoe that fits well when tried on may end up feeling too short at the end of a long day, when the foot swells. Or vice versa: one that seems roomy at home may be the right choice during a sports outing because it offers room where it is truly needed.

What size charts say and why it is worth reading them carefully

Size charts are a compass, not an exact destination. They indicate a useful equivalence between the European system, foot length, and sometimes other markets. But each brand fine-tunes the cut according to its design. That is why some manufacturers recommend checking the length in centimeters and not just the European number.

Reading a chart carefully helps avoid impulsive purchases. Some product pages show 38 2/3 and its relation to 24 cm; others show a different half size depending on the type of model. That small margin may seem technical, but in daily life it translates into less rubbing, better stability, and a more natural stride.

The best indicator is not the isolated number, but the match between measurement, last, and real sensation. If the toes touch the toe box, the size is too short. If the heel lifts easily, it is too big. If the foot sits stably, without pressure or excess play, the number is doing its job well.

How to read size 38 2/3 without making a buying mistake

The safest way to interpret 38 2/3 is to read it as an approximate 38.5 within the European system. That figure serves as an immediate reference, but the correct fit requires checking the manufacturer’s specific chart and comparing it with the foot’s actual measurement. There is no need for more mystery: precision lies in the sum of details.

Anyone buying shoes for running, walking, or moving over demanding terrain gains a lot by thinking in centimeters, not just numbers. The foot needs room to work, but also support so it does not lose efficiency. The right choice lies between both, like a taut rope at just the right point.

Understanding this equivalence avoids blind purchases and reduces returns, rubbing, and false expectations. Size 38 2/3 is not a puzzle, but an intermediate measurement useful for better fitting footwear. Properly interpreted, it works as a practical solution for those seeking precision without sacrificing comfort.