According to MedlinePlus, the normal urinary output is between 800 and 2000 milliliters a day, which indicates an hourly average in the range of 33.3 to 83.3 milliliters. This range is expected of individuals with a fluid intake of about 2 liters a day.
Dehydration, low fluid intake and chronic kidney disease are all causes of decreased urine volume, according to MedlinePlus. Higher than normal urinary output can be caused by diabetes, renal diabetes insipidus, central diabetes insipidus and some forms of kidney disease. Drinking more fluids than expected or using diuretic medications can also cause increases in urine volume.