Nursing Math Made Simple: Safe Dose, IV Drip, and Pediatric
Calculations
Essential Formulas & Conversions
Basic Conversion Factors
Weight Conversions:
• 1 kg = 2.2 lbs
• 1 lb = 0.45 kg
• 1 g = 1000 mg
• 1 mg = 1000 mcg
Volume Conversions:
• 1 L = 1000 mL
• 1 tsp = 5 mL
• 1 tbsp = 15 mL
• 1 oz = 30 mL
• 1 cup = 240 mL
Time Conversions:
• 1 hour = 60 minutes
• 1 day = 24 hours = 1440 minutes
Essential Formulas
Basic Dose Calculation:
, Dose = (Desired Dose × Volume) ÷ Dose on Hand
IV Drip Rate (gtt/min):
Drip Rate = (Volume × Drop Factor) ÷ Time in minutes
IV Flow Rate (mL/hr):
Flow Rate = Total Volume ÷ Time in hours
Pediatric Dose (mg/kg):
Dose = Weight in kg × mg/kg/dose
BSA Formula (Mosteller):
BSA (m²) = √[(Height in cm × Weight in kg) ÷ 3600]
Concentration/Dilution:
C₁ × V₁ = C₂ × V₂
Safe Dose Calculations
Steps for Safe Dose Verification
1. Convert weights to kg if needed
2. Calculate safe dose range (minimum and maximum)
3. Compare ordered dose to safe range
4. Calculate amount to administer if dose is safe
Example Problem:
Ordered: Amoxicillin 400 mg PO q8h for a 44 lb child Available:
Amoxicillin 250 mg/5 mL Safe dose: 20-40 mg/kg/day
Calculations
Essential Formulas & Conversions
Basic Conversion Factors
Weight Conversions:
• 1 kg = 2.2 lbs
• 1 lb = 0.45 kg
• 1 g = 1000 mg
• 1 mg = 1000 mcg
Volume Conversions:
• 1 L = 1000 mL
• 1 tsp = 5 mL
• 1 tbsp = 15 mL
• 1 oz = 30 mL
• 1 cup = 240 mL
Time Conversions:
• 1 hour = 60 minutes
• 1 day = 24 hours = 1440 minutes
Essential Formulas
Basic Dose Calculation:
, Dose = (Desired Dose × Volume) ÷ Dose on Hand
IV Drip Rate (gtt/min):
Drip Rate = (Volume × Drop Factor) ÷ Time in minutes
IV Flow Rate (mL/hr):
Flow Rate = Total Volume ÷ Time in hours
Pediatric Dose (mg/kg):
Dose = Weight in kg × mg/kg/dose
BSA Formula (Mosteller):
BSA (m²) = √[(Height in cm × Weight in kg) ÷ 3600]
Concentration/Dilution:
C₁ × V₁ = C₂ × V₂
Safe Dose Calculations
Steps for Safe Dose Verification
1. Convert weights to kg if needed
2. Calculate safe dose range (minimum and maximum)
3. Compare ordered dose to safe range
4. Calculate amount to administer if dose is safe
Example Problem:
Ordered: Amoxicillin 400 mg PO q8h for a 44 lb child Available:
Amoxicillin 250 mg/5 mL Safe dose: 20-40 mg/kg/day
