How to Calculate Medication Dosage: Practical Guide and Formulas

The accurate calculation of medication dosage is essential to guarantee the effectiveness of the treatment and patient safety, avoiding overdose or underdosage.

In this complete guide, you will learn the main formulas used in clinical practice and nursing routine.

1. Dosage Formula by Body Weight (mg/kg)

In pediatrics and specific treatments, the dose is adjusted based on the patient's body mass.

$\text{Dose Total (mg)} = \text{Peso do Paciente (kg)} \times \text{Dose Prescrita (mg/kg)}$

Practical Example:

If a doctor prescribes $15\text{ mg/kg}$ of a painkiller for a $20\text{ kg}$ child: $\text{Dose Total} = 20 \times 15 = 300\text{ mg}$

If the liquid medicine has a concentration of $100\text{ mg / 5 mL}$: $\text{Volume (mL)} = \frac{300 \times 5}{100} = 15\text{ mL}$

2. Calculation of Drops per Minute (Serum Drip)

For continuous infusion in syringes or serum equipment:

$\text{Gotas por minuto} = \frac{\text{Volume Total (mL)}}{\text{Tempo (horas)} \times 3}$

$\text{Microgotas por minuto} = \frac{\text{Volume Total (mL)}}{\text{Tempo (horas)}}$

3. How to Use the Interactive Calculator

To perform instant simulations without the risk of manual errors, use our Medication Dosage Calculator. Simply enter the patient's weight, recommended dose and bottle strength.