PTP Guide Step by step:Lay the garment flat on a surfaceMeasure straight from one armpit seam to the otherThat number in inches = your PTPUse this sizing guide:20″ – 21.5″ = Small21.5″ – 22.5″ = Medium22.5″ – 23.5″ = Large23.5″ – 24.5″ = XL24.5″ – 26″ = XXL26″ – 27.5″ = XXXL