Albert Thurston are a classic English Brand and their braces were worn by no less that Daniel Craig in Skyfall. 

The Braces are measured from the waistband, over the shoulder to where they attach at the back of the trouser. 

Medium are 40"/100cms, Large are 44"/110cms", and X Large are 46"/115cms

Multifit braces can be adjusted for a comfortable 'one size fits all'

Belts are measured around the waist, the length being from the tip of the buckle prong to the middle hole.