A well-fitting diaper should be tight enough around the baby's legs and waist to prevent leaks. The seams on the front, back, and sides should all be symmetrical and straight, with no slack in any area. Also, you can run your fingers around the diaper edges to ensure the leg cuffs fit nicely around your child's legs and bottom.
However, it should not restrict the baby's movement or pinch their skin. Check for signs of redness or discomfort around the groin, stomach, hips, or waist every time you change your child's diaper.
If it is not a snug fit, adjust by tightening or loosening the fasteners on either side of the tab at the diaper's waist.