My phone with case is 6.5 x 3.5 x 0.5 inches and my bicep arm is about 9.75 inches. I bought one size smaller. This headband fits my phone very well (the flip cover doesn't close all the way but I leave it open anyway), the fabric is soft, stretchy and comfortable, doesn't get wet or sweaty, the seams don't irritate. or things like zippers, velcro or buttons and it also stays on the arm. I mainly use it for running and skateboarding.
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