To find the size of your belt, you can measure a belt you already have this way or just measure your waist.
This will be the best size possible, but fortunately the belts have more than one hole 2.5 cm apart. So, if you calculate that your waist is 100 cm, you can also use a belt that is 105, or even 95 cm. You just won't push it into the middle hole
How to shorten a leather belt
You can easily shorten it yourself, as you can simply open the clasp behind the buckle to cut a piece of leather and put the buckle back on the belt.
