As a reminder, the size of a belt corresponds to the length of the belt in centimetres. And contrary to popular belief, this length does not correspond to the total length of the belt, but to the length between the beginning of the buckle and the central hole of the belt.
To find out the size of a belt, take one of your belt and measure the length between the end of the buckle and the hole you usually use. Normally this hole is marked by use, otherwise you can wear the belt and mark the hole that suits you. This will give you your belt size. It may be that the hole you usually use is not the centre hole of the belt, in which case the belt is not your size.

Belt size chart
Men
Waist size in CM Size/ France Size US (American) / Size UK (English) Belt size (in CM)
68/72 36 26 65-70
72/76 38 28 70-75
76/80 40 30 75-80
80/84 44 34 80-85
84/88 46 36 85-90
92/96 48 38 90-95
96/100 50 40 95-100
100/104 52 42 100-105
104/108 54 44 105-110
108/112 56 46 110-115
112/116 58 48 115-120
116/120 60 50 120-125