A belt is a small purchase that does a lot of work. Leather is the most popular material because it tolerates bending and tightening and moulds to the wearer over time.
Width
Formal dress belts are usually about 28 to 32 mm wide with a polished metal buckle, while casual belts run about 35 to 42 mm.
Sizing
Choose a belt that fastens on a middle hole so you have room either way. Many belts also allow the buckle to be adjusted.
Houses known for belts and buckles
Gucci was founded in Florence in 1921 by Guccio Gucci, and its double-G logo was introduced in 1964 for belt buckles and other accessories. Ferragamo was founded in Florence in 1927 by Salvatore Ferragamo, and its Gancini motif is a signature element. Hermès began in Paris in 1837 as a saddlery and harness maker.
What to inspect
Look at the leather edges, stitching, hole punching and hardware finish. A well-made belt should feel firm without cracking when flexed.
Sources: Wikipedia: Belt, Gucci, Ferragamo and Hermès.
For finishing touches, browse the shop.