Open the Size Chart. Determine if the product uses body or garment measurements. The parameters used can identify this. They are garment measurements if the measurements are in halves, like half chest or half waist. If they are simply waist or chest, then they are body measurements.
A. WAIST
Measure around your waist, keeping the tape level and straight. Keep one finger between the tape and the body.
Pick a similar garment that you already own that fits you well. Lay the garment out on a flat surface and start measuring.
A. HALF WAIST
Measure the garment flat from one side seam to the other at the waist level, at the top of the pants.