If your panty fits correctly, you can avoid ride-up, sagging, and pinching elastic. For proper panty fit, measure you waist and your hips.
Getting the Perfect Panty Fit
Measure your waist by placing the tape measure around the natural indentation in your waist. Bend to one side to make the indentation more obvious. Measure the fullest part of your hips, keeping the tape parallel to the floor. If your measurements indicate two different sizes, choose the larger size.