Dosage Calculator

Created by Luciano Mino
Based on research by
University of South Australia Dosage Calculation - WorksheetSee 1 more source
Cookson KL. Dimensional analysis: calculate dosages the easy way. Nursing (June 2013)
Last updated: Jul 08, 2022

The dosage calculator will help you obtain the appropriate medication dosage to take when the dosage of the drug depends on the patient's body weight.

Within a few paragraphs, we will explain:

  • How to calculate medication dosage by weight;
  • How to use the dosage by weight formula;
  • How to calculate liquid medication dosage; and
  • More about dosage calculation.

Dosage calculation

There are several ways to calculate the medication dosage for a patient, and they all depend on the type of treatment the patient will receive.

Some medications require a single specific dosage, and your doctor will set the dosage for you for others. The dosage may also depend on the concentration of the drug's active compound, so you can't use this dosage calculator for any of these drugs.

This tool is intended for drugs where their dosage depends on the patient's body weight.

Dosage calculation formula

For drugs that depend on the patient's body weight, we can use the following drug dose calculation formula:

dose=weight×dosage\text{dose} = \text{weight} \times \text{dosage}

where:

  • weight\text{weight} is the patient's weight in the appropriate unit (kg or lb).
  • dosage\text{dosage} is the prescribed amount of drug in mg per kg of body weight. This number should be visible in the medication's box or prescription.
  • dose\text{dose} is the total amount of medication you need to take.

However, if your medication is in liquid form, you should use another dosage calculation formula:

liquid dose=dosedrug concentration{\footnotesize \text{liquid dose} = \frac{\text{dose}}{\text{drug concentration}}}

where:

  • drug concentration\text{drug concentration} is the amount of active substance per drug volume. Usually expressed in mg per ml.

🔎 Concentration and density are not the same thing. Check our density calculator and density converter to learn more about this measure.

How to calculate medication dosage by weight using the drug dose calculation formula

We've already shown how to calculate medication dosage by weight and how to calculate liquid medication dosage. Let's walk through each step to calculate dosage by weight:

  1. Find the correct dosage of the medication. Suppose 3 mg per kg of body weight.
  2. Weight yourself. Let's say the scale shows 70 kg.
  3. Multiply your weight by the dosage according to the dosage by weight formula. In our example 3 * 70 = 210 mg. This means you should take 210 mg of the medicine.
  4. If your medication is in liquid form, write down the concentration of the drug. Let's say 2 mg per ml.
  5. Finally, take the dose you calculated in step 3 and divide it by the concentration: 210 / 2 = 105 ml. So, you should take 105 ml if you're taking this medication in liquid form.
Luciano Mino
Your weight
lb
Dosage
mg
/kg
Frequency
once per day
Total daily dose
mg
Liquid medicine
Medicine concentration
mg/mL
Total liquid dose
ml
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