Weight-Based Dose Calculator (mg/kg) with Safe Dose Check
Pediatric and many adult doses are ordered per kilogram. Enter the weight and the ordered mg/kg, or switch to checking whether an ordered dose is in its safe range.
Shows the work. Answer, formula, and numbered steps, rounded the way nursing exams expect. For study and exam practice, not for patient care.
Formula
Dose = mg/kg × weight in kg.
Fill in the fields and press Calculate to see the answer and every step.
For study and exam practice, not for patient care.
Rounding: A weight in pounds is converted and rounded to the tenth of a kg first. Doses and volumes round to the hundredth.
Terms: Weight-based dosing, Safe dose range
Worked examples
Vancomycin 10 mg/kg/dose IV every 6 hours is ordered for a child who weighs 31.1 kg.
- Solve for
- Dose from mg/kg
- Weight
- 31.1 kg
- Ordered dose per kg
- 10 mg/kg
Formula Dose = mg/kg × weight in kg.
- Dose = 10 mg/kg × 31.1 kg = 311 mg.
- 311 mg is exact, so no rounding is needed.
Answer 311 mg
Azithromycin 5 mg/kg/dose PO daily is ordered for a client who weighs 53 kg. Available: 200 mg/5 mL.
- Solve for
- Dose from mg/kg
- Weight
- 53 kg
- Ordered dose per kg
- 5 mg/kg
- Have
- 200 mg
- Vehicle
- 5 mL
Formula Dose = mg/kg × weight in kg.
- Dose = 5 mg/kg × 53 kg = 265 mg.
- mL = 265 mg ÷ 200 mg × 5 mL = 6.625 mL.
- Round to the nearest hundredth: 6.63 mL.
Answer 6.63 mL
FAQ
How do you calculate a weight-based dose?
Convert the weight to kg (lb ÷ 2.2), then multiply by the ordered amount per kg. For a per-day order, divide the daily total by the number of doses.
How do you check a safe dose range?
Multiply the weight in kg by the low and the high end of the recommended range per kg. If the ordered dose falls between them, it is in range; if not, hold it and contact the prescriber.
Should I round the weight before calculating?
This calculator rounds a converted weight to the tenth of a kg, as most nursing programs do, then rounds only the final dose. Follow your program's rule if it differs.