I wear XL in both Novara arm warmers and PI knee warmers.

42.54cm (16.75") bicep
20.95cm (8.25") at cuff
Neither measurement is too tight for comfort on the arm warmers, although the length is a little short for me and the cuff hits me above my wrist where the measurement is wider. Few companies design stuff around people with a 37" shirtsleeve.

69.85cm (27.5") quad
39.37cm (15.5") at cuff
I wear the knee warmers with the upper cuff about 4cm (~1.5") into the leg of my shorts. The lower cuff sits mid-way between my knee and the widest part of my calf. The gripper isn't binding there, but it does hold the entire thing from slipping upward toward my knee and bunching up the fabric.