Medication Dosage Calculator

A weight-based medication dosage calculator multiplies a per-kilogram dose (the standard for pediatric and many critical-care medications) by the patient's body weight to produce a single-dose amount. It then multiplies by frequency to give the total daily dose, and — when a liquid concentration is provided — divides by that concentration to give the volume in milliliters to administer.

This calculator is for educational reference only and is not medical advice. Real prescribing requires consideration of age, organ function, drug interactions, and product-specific labeling. Always verify any dose with a pharmacist or licensed healthcare provider before administering medication, and follow the dosing chart that ships with the product.

A 22 lb (10 kg) toddler is prescribed amoxicillin at 25 mg/kg twice daily, using a suspension labeled 250 mg / 5 mL (50 mg/mL):

• Single dose: 10 kg × 25 mg/kg = 250 mg
• Daily total: 250 mg × 2 = 500 mg/day
• Volume per dose: 250 mg ÷ 50 mg/mL = 5 mL

Another example — pediatric ibuprofen at 10 mg/kg every 6 hours for an 18 kg child:

• Single dose: 18 × 10 = 180 mg
• Daily total (4 doses): 720 mg/day — comfortably under the 40 mg/kg/day pediatric maximum (720 mg)
• Using 100 mg / 5 mL (20 mg/mL) suspension: 180 ÷ 20 = 9 mL

• Pediatric dosing — almost all over-the-counter and prescription pediatric meds use weight-based ranges.
• Liquid suspensions — converting a milligram dose into a measurable volume in milliliters.
• Cross-checking a prescription — verifying the pharmacy's calculation before giving the first dose.
• Veterinary dosing references — animals are almost always weight-dosed (though species-specific factors apply).
• Anesthesia, oncology, and ICU drips — where mg/kg or mcg/kg/min dosing is the norm.

• Unit confusion (mg vs. mcg vs. g). A factor-of-1000 error in either direction can be lethal — confirm the prescription unit, the bottle unit, and the calculator unit all match.
• Forgetting maximum doses. Most pediatric drugs cap at the adult dose; a 70 kg adolescent doesn't necessarily get the full mg/kg multiplied through.
• Weight in the wrong unit. Entering 33 lbs as if it were 33 kg over-doses by 2.2×. The calculator's unit toggle prevents this only if you set it correctly.
• Mixing concentration formats. "250 mg / 5 mL" is 50 mg/mL, not 250. Always normalize to mg per single mL before dividing.
• Skipping organ-function adjustment. Renal or hepatic impairment can require dose reduction of 25–75%; weight alone won't reflect that.
• Using household spoons. A "teaspoon" varies from 2.5 to 7 mL; always use a calibrated oral syringe or dosing cup.