lululemon Go Further Seamless Running Arm Sleeves

How to measure:

Chest / Bust: Measure around the fullest part of your chest, keeping the tape horizontal and comfortable.
Waist: Measure around your natural waistline, keeping the tape comfortably loose. For men's bottoms, if you typically wear a 32 in pants, you'll likely be a 32 in our pants.
Hip: Measure around the fullest part of your hips.
Bra band: Run a tape measure around your ribcage right under your bust. Bra support comes mostly from the band, so it should fit snug.

If you're between sizes, consider sizing up for a more relaxed fit or sizing down for a tighter performance fit. Every body is different, so use these charts as a starting point.