The shoe sizes are written only as numbers from 5 to 9; is a 245mm foot a size 5 or 6?
I know my foot length in mm, but because the size is shown as a single number, I cannot tell where it fits. Especially if the value borders two intervals, it is hard to decide which one to choose.
Because 245mm falls across both intervals for 5 and 6, it cannot be determined as one side based on the size chart alone.
Let us examine the numbers first. VIBRAM SNEAKERS are sneakers made with a Vibram outsole[1], and the sizes correspond to 235–245 for 5, 245–255 for 6, 255–265 for 7, 265–275 for 8, and 275–285 for 9[2]. Instead of a single number pointing to one specific measurement, it is structured so that a number covers an entire foot length interval.
When intervals are connected like this, the end of the preceding interval and the start of the next interval meet at the exact same value. A 245mm foot sits at both the end of 5 and the start of 6[3]. The situation is the same for 255mm, 265mm, and 275mm. Which side is recommended in this case is not separately stated in the official size guide.
Therefore, a foot that falls on the boundary needs one more personal criterion. It is common to measure foot length standing with your heel against a wall, measuring both feet in the afternoon when feet are most swollen, and using the longer side as your reference. If you often wear thick socks or have wider feet, the larger number often fits better; if you wear thin socks and have narrower feet, the smaller number often fits less loosely.
To summarize, rather than indicating a single exact size, this chart shows whether your foot sits in the middle of an interval or borders the end. If it is in the middle, there is nothing to worry about; if it borders the end, your socks and foot width will determine the remaining choice.
Which size the brand recommends for a value where 2 intervals overlap like 245mm, as well as the standard measurements for foot width, have not yet been confirmed.