For something that’s supposed to be relatively simple, shoe sizing can definitely get incredibly messy. Why is shoe size not a ratio? Why doesn’t it feature as a variable in charts? In order to understand the answer, you have to take a look at the manner in which shoe sizing methodologies work.

Sizing Systems
Shoe size charts vary because different sizing systems may be used. These systems are also utilised in the world of shoemaking, ensuring that the particular product would be a good match for a person looking for a particular number.

The most common system being used is the International Standard ISO 9407: 1991. Also known as Mondopoint, it relies on the length of the foot for the calculation of the right size. In occasions, the width of the foot will also be measured in millimetres to make sure that the fit is ideal.

The size is usually presented in the form of two numbers – 275/100, which means that the length of the foot is 275 millimetres and the width is 100 millimetres.

Because it relies on two measurements, the Mondopoint system is the one that ensures the highest level of accuracy when it comes to shoe size.

A different system is used in the UK and Ireland. In this instance, the length of the foot will once again be taken into consideration when it comes to determining the size. The length, however, is measured in the so-called “barleycorn” a unit that consists of 1/3 inch increments.

In the US and Canada, there may be several systems used to determine shoe size. The traditional system is rather similar to the one used in the UK. The smallest number in the UK is a zero. In the US and Canada, numeration starts from a one. This is the main reason why there could be a difference between UK and US sizes.

Children shoe sizes in the US are calculated following a simple formula. They are equivalent to the shoe sizes for men plus 12 1/3. Though in some systems there may be the difference between the numeration for boys and girls, the standard measuring scale offers just one option that is not gendered.

Why are Shoe Size Charts Different?
Based on the sizing methodology explanation provided in the first part of the article, it becomes easier to understand why shoe size charts may be so different from each other.

In essence, all of the systems begin with a measurement of the length of the foot. The increments in which this measurement is taken and the smallest number in the respective scale, however, vary from one measuring system to another.

In Europe, shoe makers use 2/3 of a centimetre as the increment in which shoe sizes progress. The shoe size in European systems is, in essence, the length of the foot in Paris points (the name of the increment). To get the right size, you can simply multiply the length of your foot in centimetres by 1.5. Thus, a man whose foot measures 29 centimetres should wear the European shoe size 43.5 (or 44 if the particular brand does not offer halves).

The entire confusion and the difficulty stem from the fact that there are shoemakers across the world who have decades, even centuries of tradition in this form of manufacturing. They’ve been using a certain measuring system for a long period of time, which created traditions. This is the reason why the world doesn’t have a universal measuring system that everybody can rely on.

The good news is that consumers have it a little bit easier today. There are numerous sizing and conversion charts that can be used to make sense of the entire mess. Once you have a good idea about the length of your foot (whether in centimetres or in inches), you can figure out which one of the numerous international numbers is a good match.

Finally, remember that certain manufacturers may have a system of their own. In this instance, the chart will not correspond 100 percent to the international standards you usually come across. Such shoe making companies will always provide their sizing chart that you can use to make a purchase. Don’t take the international systems for granted – always double check to make sure that the respective manufacturer is using standard units.