Correction: My apologies Gentlemen, I checked my UM underwear and the size is XL not L is I alluded to above. The important message is that the UM size chart is accurate relative to the waist measurement rather than whether you normally buy S,M,L etc. so go with where your measurement sits on...
When ever I buy UM, I simply go with the size chart and order the actual waist measurement. I normally buy size M for a 33 Inch waist but this equates to large or even extra large for UM but I prefer my thongs to be on the tighter side so I stick with size L.