The #013 style of Texas Jeans have a comfort band sewn into the waist.  This allows for some stretch in the waistband and a snug fit when moving or bending.  The 2 numbers for the waist size indicate actual waist size and stretched size  ( 34" (36") ) would mean a 34 " waistband that can stretch to at least 36" comfortably.  When ordering be aware that over time and washing the jeans may grow slightly in the waist.