In order to analyze of the bilirubin levels in adults are normal or not, the doctor will need to look at the values of all three, direct bilirubin, indirect bilirubin and total bilirubin. Given below is the normal bilirubin range in adults: 1  Direct bilirubin: 0.1 mg/ dl to 0.3 mg/ dl (1.7 mmol/ l to 5.1 mmol/ l).n order to analyze of the bilirubin levels in adults are normal or not, the doctor will need to look at the values of all three, direct bilirubin, indirect bilirubin and total bilirubin. Given below is the normal bilirubin range in adults: 1  Direct bilirubin: 0.1 mg/ dl to 0.3 mg/ dl (1.7 mmol/ l to 5.1 mmol/ l).