Medication Dosage Calculator
Calculate medication dosage.
Input
Result
What is a Medication Dosage Calculator?
A Medication Dosage Calculator computes the correct amount of medication to administer based on factors such as patient weight, prescribed dose per kilogram, and drug concentration. It helps reduce calculation errors that can lead to underdosing or overdosing.
How to calculate medication dosage manually (the formula)
Weight-based dose: total dose (mg) = dose per kg (mg/kg) × patient weight (kg).
Liquid volume: volume (mL) = total dose (mg) ÷ concentration (mg/mL).
Always double-check that units are consistent. Convert pounds to kilograms by dividing by 2.2046 if needed.
Example calculation
A child weighing 20 kg is prescribed 5 mg/kg of a medication. The liquid concentration is 125 mg/mL. Total dose = 5 × 20 = 100 mg. Volume to administer = 100 ÷ 125 = 0.8 mL.
Common mistakes
- Mixing up mg and mL — Milligrams measure drug mass, millilitres measure liquid volume. They are not interchangeable without knowing the concentration.
- Forgetting to convert pounds to kilograms — Weight-based dosing uses kilograms. Using pounds directly gives a dose roughly 2.2 times too high.
- Misreading the decimal place — A 0.1 mL error in a paediatric syringe can be significant for potent drugs. Always verify decimal placement.
Frequently asked questions
How do I calculate a medication dosage?
Dosage depends on the prescribed dose per unit of body weight: total dose = dose per kg × patient weight in kg. Always check the prescription and units carefully.
What is the difference between mg/kg and fixed dosing?
mg/kg dosing scales the amount to the patient’s weight, common for children and certain drugs. Fixed dosing uses the same amount for every adult regardless of weight.
How do I convert mg to mL for liquid medications?
Volume (mL) = desired dose (mg) ÷ concentration (mg/mL). For example, 250 mg of a 125 mg/mL solution requires 250 ÷ 125 = 2 mL.
What is a loading dose?
A loading dose is a larger initial dose given to quickly reach therapeutic blood levels. It is followed by smaller maintenance doses. The formula is: loading dose = target concentration × volume of distribution.
Why is weight important in pediatric dosing?
Children’s metabolic rates and body sizes vary enormously by age. Weight-based dosing ensures the amount is safe and effective for each child’s size.
Should I use this calculator instead of a doctor’s advice?
No. This calculator is for educational reference only. Always follow the dosage prescribed by your healthcare provider or pharmacist.