To determine if a diaper is too small, check for tightness or gaps. If you see creases or indentations on your baby’s skin, the diaper is too small. Use a measuring tape to ensure the diaper is the correct size for your baby’s waist, thighs, and hips. Consider the material and activity level when choosing a diaper. Regularly monitor the fit and adjust the size as needed for your baby’s comfort and well-being.