1. Most Belts Have Holes About 2.5 cm Apart
Even if you buy from different stores, the spacing between holes is similar. Explanations from clothing stores state that the distance between holes on most belts is 2.5 cm. [1] While this is based on individual answers, some voices say, "It is not a fixed rule, but most are 2.5 cm." [6]
This seems to be a custom rather than a law. It is not clear if there is a specific standard or law that sets this spacing. For now, we can only say that "most belts are like this."
2. Could Inch Measurements Explain the 2.5 cm Spacing?
One clothing store explains that when Western clothing culture arrived in Japan during the Meiji era, inches were used for clothing measurements. Because of this, it is "said to be" that holes spaced 1 inch (about 2.54 cm) apart became common. [1]
This explanation comes from a store's commentary and has not been verified by records from that time. An American leather belt shop also writes that they punch holes at 1-inch intervals. [2] Since this is not just a Japanese situation, it is safe to think, "The inch custom might have been widely shared."
3. Why Belts Often Have an Odd Number of Holes
Clothing store explanations list odd numbers of holes, such as 5 or 7. The reason given is that fastening at the middle hole gives a better visual balance. [1] An American leather belt shop also states that the standard is 5 holes (2 on the long side, 2 on the short side, and 1 in the middle). For belts longer than 50 inches, they use 7 holes. [2]
Another store says you fasten using the 3rd hole of the 5. They explain that the belt size label is also determined based on this 3rd hole. [3]
4. Belt Size Is the Length to the Middle Hole
It is not the total length of the belt. Store guides state that belt size is expressed as the length from the base of the buckle to the middle belt hole. [4] In one store's chart, a 32-inch size is 81 cm, with a waist range guide of 79 to 86 cm. [4] Please view this as an example, as the corresponding range differs by store.
Because the design has a center hole as the reference, a single size number can represent the adjustment range, including the holes above and below it.
5. How the Holes Above and Below the Middle Hole Adjust the Fit
An American leather belt shop explains that you mainly use the center hole, and use the surrounding holes to handle changes in weight due to seasons. [2]
Looking at the numbers, a domestic store's chart shows that an 80 cm size adjusts from 74 to 86 cm, and an 85 cm size adjusts from 79 to 91 cm. [3] This is 6 cm above and below the center. If we assume the adjustment range is covered by 2 holes above and below, each step is about 3 cm, which is slightly wider than 2.5 cm. Since this is a calculation from a chart, not a direct measurement, the difference in hole spacing by store might be one reason.
6. Why Fixed 2.5 cm Spacing Can Feel Too Loose or Too Tight
When holes are fixed at 2.5 cm intervals, depending on body size or clothing thickness, loosening one step can be too loose, and tightening one step can be too tight. A Lifehacker Japan article calls this a "dilemma." [5]
One answer introduced is the slide-type (stepless) belt. The article explains that it can be adjusted in 1 mm units. [5] This form removes the "steps" that hole spacing had decided.
7. How to Investigate Belt Holes Yourself
Things you can do today: Count the holes on a belt you have and measure the spacing with a ruler. Put a sticky note on the middle hole to mark it. Check how many holes away from that mark you usually fasten. This helps you understand the relationship between the position that fits your body and the design's reference point.
If you want to expand your research: Pages on "how to choose sizes" from stores that sell belts or clothing shops are available in Japanese. Comparing how hole spacing and adjustment ranges differ by store can be fun.