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. CHEST
Measure around the fullest part of the chest, 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 CHEST
Measure across the chest, side seam to side seam, 2cm below where the sleeve joins the body of the garment.