# Dosage Calculator

Created by Łucja Zaborowska, MD, PhD candidate and Łukasz Białek, MD
Reviewed by Dominik Czernia, PhD candidate and Jack Bowater
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: Sep 16, 2022

The dosage calculator finds what dose of a medication is appropriate for your weight. It can also recalculate the dosage expressed in mg/kg into doses of liquid medication.

Read on to learn what the drug dosage calculation formula is and how to use it. With our text, you will also learn more about the various different kinds of dosing which you may encounter when using different medications. You will also find out what the advantages are of adjusting the dose to the patient.

Are you looking for a healthy dose of antipyretic medication for kids? Make sure to take a look at our ibuprofen dosage calculator and the paracetamol dosage calculator!

We try our best to make our Omni Calculators as precise and reliable as possible. However, this tool can never replace a professional doctor's assessment.

## Dosage forms

Depending on the route of administration, dosage forms come in several different types. The most popular route of administration is oral, however, in some medical situations this route is unavailable, ineffective or associated with a high number of adverse reactions. That is why patients may receive drugs through parenteral means (this includes: subcutaneous, intramuscular, intraosseous, intravenous, etc.). Moreover, some drugs are only given topically – they're applied directly onto the skin or eye, into the rectum or vagina, or as an inhalation.

You should know that the route of administration of a drug dramatically influences its dosage and efficacy. You should thus always check if you are administering the appropriate drug to the appropriate person through the appropriate route in the appropriate dose!

## What is an appropriate dose?

When treating a patient, or just taking a medication by yourself, we always need to wonder what is the exact dose of the drug we choose. And the truth is that we dose (or should dose) nearly everything in our life, from cooking dinner to taking medications! However, regarding drugs, there are certain different kinds of dosing that depend on the specific drug and/or the patient.

1. One dosage

Drugs with one fix dosage are the easiest to use; you just take it and forget about it (e.g., vaccines). You don't need to use any dosage calculation formulas!

2. Different, fixed dosages

The dosage of these drugs is usually set by the doctor according to the patient's needs or age (e.g., hypotensive drugs). In this case, you also don't have to worry about medical dosage calculations!

3. Different, variable dosages

In this case, the doctor usually suggests the patient a sample dosage; the patient then modifies it according to his/her needs and the situation (e.g., insulin).

4. Blood concentration-dependent dosages

This is a relatively small group of drugs. The doses are different depending on the concentration of the drug's active compound in the serum (e.g., vitamin K antagonists, lithium, etc.).

5. The dosage of the drug depends on the patient's body weight

The dose of the drug depends on the weight of the patient. It means that two patients with the same disease may receive a different amount of the same drug!

Our dosage calculator will help you calculate appropriate doses of this kind of drugs!

## Why do we need to calculate doses?

In the sixteenth-century Swiss scientist Paracelsus said:

"All substances are poisons; there is none which is not a poison. The right dose differentiates a poison and a remedy."

This sentence still holds today. We know that every substance, especially drugs, may be toxic if given in an inappropriate dose. An example of a well known but potentially toxic substance is Tylenol (paracetamol). This is why we should perform our dosage calculations carefully and accurately. This is especially critical when administering drugs to children, as a slight mistake in the dose may cause a significant change in the effect of its action. The usage of a pediatric dose calculator seems to be a responsible choice that reduces the risk of a mistake!

Contemporary scientists are also looking at the issue of drug dosage. There are plenty of ongoing clinical trials in which different doses of the drugs are being compared. Moreover, there are more and more scientific data suggesting that individually performed dosage calculations (not only in pediatric patients) improve patient survival when compared with a standard treatment of fixed doses.

For instance, in 2016 a group of scientists from France published an in which they summarized the results of their clinical trial on patients with metastatic colorectal cancer (cancer of large bowel in the IV stage of the disease – with metastases). The group that was treated with an individually adjusted dose of fluorouracil (antimetabolite drug used in the treatment of many cancers, including colon cancer) had a better response to the therapy, a higher survival rate and a lower grade of toxicity, than those treated with standard doses.

As you can see, it's worth using drug dosage calculators!

## Calculating medication dosage by weight

Medical dosage calculations that consider a patient's weight are very common in obese patients and on pediatric wards. It's easy to imagine that the weight of the body of an adolescent may be 40 times larger than that of a newborn baby, so we hope you can see the need to dose drugs accurately.

Moreover, some specific drugs for adults need to be dosed according to the patient's weight. These include heparin, antibiotics, and muscle relaxants.

## Dosage calculation formulas

If you want to calculate the dose of a medication, you need to use the following equation:

$Dose = Weight × Dosage$

Where:

• Weight — Patient's weight, expressed in kg or lb. It is very important that you input an accurate result;
• Dosage — Prescribed amount of drug in mg per kg of body weight. You can usually find this number on the medicament box or on the prescription; and
• Dose — Total amount of medication you need to take.

The situation gets more complicated if your medicine is in liquid form. After all, how are you supposed to know how many ml of your drug you are meant to take to ingest, for example, 50 mg of the active substance? Our dosage calculator can help you with this as well. All you have to do is use the following formula:

$Liquid\ dose = Dose / Medicine\ concentration$

Where:

• Medicine concentration — Amount of active substance per a given volume of your drug. It can be expressed in mg per ml.

This function of our dosage calculator is especially useful when giving fluid drugs (e.g., syrup) to children and in hospitals, where many drugs are given to the patient not only orally but intravenously. Conversion from mg to ml is essential in situations like these!

## How to calculate drug dosage

If you want to find what the appropriate dosage of a drug is for your body weight, you need to follow these steps:

1. Determine the dosage of the medication. Let's say the appropriate dosage of the active substance is 2 mg/kg of body weight.

2. Weigh yourself. Let's assume you weigh 80 kg.

3. Multiply these two values to get the dose of medication in mg: 2 * 80 = 160 mg. You need to take 160 mg of active substance.

4. What if your medication is liquid? Type the concentration into the proper box. Let's say the concentration of your medicine is 2 mg/ml.

5. Divide the dose by the medicine concentration to obtain the liquid dose: 160 / 2 = 80 ml.

Make sure to take a look at our drug conversion calculators, such as the steroid and opioid conversion calculators!

Łucja Zaborowska, MD, PhD candidate and Łukasz Białek, MD
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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