Phenoxymethylpenicillin Dose Calculator Weight (kg) Age Years Months Choose Indication General Dosing Strep A Dosing Choose Phenoxymethylpenicillin Strength Phenoxymethylpenicillin 120 mg/5 mL Phenoxymethylpenicillin 250 mg/5 mL Dose in millilitres Dose in milligrams General dosing: for ages 1 month to 18 years Strep A: for ages 3 to 18 years Calculator written by Dr Jeremy Steinberg, GP. Contact for suggestions