Free Tool
Weight-Based Dose Calculator (mg/kg)
Calculate the total dose from a per-kilogram order and patient weight.
Formula
total dose = patient weight (kg) × dose per kg
Convert pounds to kg: divide by 2.2
Result
Enter values above to calculate.
Worked example
Scenario: Order: Cefazolin 25 mg/kg IV. Patient weighs 154 lb.
- 1Convert weight to kg: 154 lb ÷ 2.2 = 70 kg.
- 2Apply formula: 70 × 25 = 1,750.
Administer 1,750 mg.
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When to use this calculation
Weight-based dosing is the standard for pediatric medications and many adult drugs where dose has to scale with body size (antibiotics, anticoagulants, chemotherapy, anesthetics). The calculation itself is trivial — multiply weight by the per-kg dose — but the conversion step is where most errors happen: weights documented in pounds must be converted to kilograms (lb ÷ 2.2) before applying the per-kg dose.
After calculating the total mg, you usually need a second step to convert mg to mL using the medication's concentration. Don't skip the safety check: compare your calculated dose against the maximum single dose listed in a drug reference. A correctly-computed weight-based dose that exceeds the maximum safe dose is still a medication error.