1. If you are estimating your size then as a rule of thumb - go one size up from you jeans size. Wearing a jeans in size 34 - then your belt size is 36!
2. Measuring an existing belt is the more accurate method of getting your size just right.
Do's: Measure from the very start of the leather strip (where the buckle meets the leather) up to the hole that fits you best in inch. This is the size you order.
Don'ts: Don't measure the total belt length and don't include the buckle.