Step 1: Convert inputs to common units.
Step 2: Solve equation.
Daily Dose = Weight (kg) × Dose (mg/kg)
Daily Dose = 70 × 5 = 350 mg Per Dose = 350 mg ÷ 3 = 116.67 mg
Result = 116.67 mg per dose
Weight-based dosing calculates the appropriate medication dose according to a patient's body weight. This method is especially important in pediatrics, oncology, and critical care where standardized adult doses may be unsafe or ineffective.
The prescriber orders a dose in mg/kg (milligrams per kilogram of body weight). The nurse multiplies this by the patient's weight to determine the total daily dose, then divides by the number of daily administrations.
Calculate Dosage by Weight ↑A child weighing 25 kg is prescribed amoxicillin at 40 mg/kg/day divided into 3 doses.
Daily total = 25 kg × 40 mg/kg = 1,000 mg/day
Per dose = 1,000 / 3 = 333.3 mg per dose
Standard adult doses assume an average body size. Patients who are significantly lighter or heavier may be under-dosed (reducing efficacy) or over-dosed (increasing toxicity risk). Weight-based dosing tailors the medication to the individual patient.
Most medications use actual body weight. However, certain drugs (e.g., aminoglycosides, some chemotherapy agents) use ideal body weight or adjusted body weight for obese patients. Always check the specific drug monograph or consult the pharmacist.
Even when dosing by weight, never exceed the maximum recommended dose for any single administration or daily total. If the weight-based calculation yields a dose above the maximum, cap it at the maximum and document accordingly.