How can you tell if your liver is enlarged?

I doubt you can do so yourself. Doctors are taught methods to estimate liver size by physical exam. Some rely on an ultrasound/x-ray/CT or MRI finding that can be quite accurate.

What makes you feel that your liver is enlarged. If you no health issues, it would not warrant investigation. As Dr. Ferguson stated, it would require physical examination on imaging studies. For healthy diet: http://www.choosemyplate.gov/., exercise 30 minutes/day, drink enough water daily so your urine is mostly colorless, have safe sex, no tobacco alcohol weed or street drugs.

Enlarged liver may be felt as fullness of right upper abdomen. Some have symptoms of disease as hepatomegaly is a sign of an underlying problem. Symptoms can be abdominal pain, fatigue, nausea, vomiting, jaundice. One can reduce the risk factors for it, drink in moderation, avoid large supplements, avoiding overweight. Limit contact with chemicals. Hope it helps.