My baby is eight months old and weighs twenty pounds. I was wondering what dosage of Infant Tylenol (acetaminophen) I should be giving her in milliliters?

4.3 ml. It is better to use a milliliter dropper in order to be more precise. You can dose tylenol (acetaminophen) up to 15 mg/kg. 20 lbs is about 9 kg so you can give about 130-140 mg based on weight which is about 4.3 ml by mouth.
Tylenol (acetaminophen) dose. 1 teaspoon . Acetaminophen is dosed approximately 1 teaspoon per 20 pounds. :)