Medication Calculator
Fast, accurate, and free online Medication Calculator tool that runs directly in your browser.
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Other tools you may find usefulPrecise drug dosing - the foundation of safe pharmacotherapy
Drug dosing is a key element of the treatment process, on which both therapeutic effectiveness and patient safety depend. In medicine and pharmacy, there is a rule that a chemical substance in the right dose is a drug, but in excess it becomes a poison (dosis facit venenum). Correctly calculating drug doses requires absolute precision and eliminating mathematical errors, which can easily occur during manual calculations, especially in stressful situations. This applies especially to medicines in liquids, injection solutions, antibiotics in suspension and medicines given to children and the elderly.
Our professional online drug and solution concentration calculator was created to support patients, parents and medical staff in precisely converting milligrams to milliliters, calculating doses based on body weight and facilitating the correct interpretation of medical recommendations.
Basic units of measurement used in drug dosing
In pharmacy and medicine, units of mass and volume are used in the decimal system:
- Gram (g):basic unit of mass in the recipe.
- Milligram (mg):1/1000 part of a gram (1 g = 1000 mg). Most tablet drug doses are given in milligrams.
- Microgram (mcg/µg):1/1000 part of a milligram (1 mg = 1000 mcg). Used with very strong substances (e.g. thyroid hormones, steroids).
- Milliliter (ml):unit of fluid volume.
How to convert the percentage of a solution to milligrams?
Many liquid medicines have their concentration indicated as a percentage (e.g. 1% drug solution). This means that there is 1 gram of active substance in 100 ml of liquid:
1% concentration = 1 g of substance in 100 ml = 10 mg of substance in 1 ml
The table below shows the conversion of percentage concentrations of solutions into the amount of substance in 1 ml:
| Percentage concentration of solution (%) | Amount of substance active substance in 100 ml of solution | Amount of active substance in 1 ml of solution (mg/ml) | Typical example of medical use |
|---|---|---|---|
| 0.9% | 0.9 g | 9 mg/ml | Physiological saline (NaCl solution) for nebulization and drips. |
| 1% | 1.0 g | 10 mg/ml | Local anesthetics (e.g. lidocaine). |
| 2% | 2.0 g | 20 mg/ml | Analgesic syrups with a higher dose of the substance. |
| 5% | 5.0 g | 50 mg/ml | Glucose solution for intravenous infusion. |
| 10% | 10.0 g | 100 mg/ml | Electrolyte concentrates or strong antiseptic solutions. |
How to calculate the drug dose based on the patient's weight?
The formula for a single dose of medication based on the patient's body weight is as follows:
Dose (mg) = Body weight (kg) × Recommended unit dose (mg/kg)
For example: If the recommended dose of an antibiotic is 20 mg per kg of body weight per day and the patient weighs 15 kg, then the total daily dose of the medication is:15 kg × 20 mg/kg = 300 mg. If the medicine is to be given in 3 divided doses, each single dose will be 100 mg.
Frequently asked questions (FAQ)
How to convert milligrams (mg) to milliliters (ml)?
To perform this calculation, it is necessary to know the concentration of the drug (how many mg of the substance are in 1 ml of liquid). The formula is: Volume (ml) = Dose (mg) / Concentration (mg/ml).
What does the abbreviation "mcg" or "µg" mean on the medicine package?
These abbreviations stand for micrograms. 1 microgram is one millionth of a gram or one thousandth of a milligram (1 mg = 1,000 mcg). The mistake of confusing mg with mcg can result in a thousand-fold overdose of the drug.
What is the difference between a therapeutic dose and a maximum dose?
The therapeutic (therapeutic) dose is the amount of a drug that produces the desired therapeutic effect in most patients. The maximum dose is the largest amount of a substance that can be safely administered to a patient at a given time (e.g. within 24 hours) without the risk of serious poisoning.
How to calculate the dose of medicine in drops?
In pharmacy, it is standardly assumed that 1 ml of aqueous solution is approximately 20 drops. However, for thick or alcoholic solutions, this number may be different (up to 40-50 drops in 1 ml). Always check the drug leaflet for the exact conversion between drops and milligrams.
What are loading and maintenance doses?
A loading dose is a higher dose of medicine given at the beginning of treatment to quickly achieve therapeutic levels of the substance in the body. A maintenance dose is a lower dose taken regularly to maintain this level.