Nursing Dosage Calculations and Conversions

Basic Conversions & Calculations

• To convert 2.5 grams to milligrams, the equivalent dosage is 2,500 mg.
• To infuse 500 mL of D5W over 4 hours, the flow rate is 125 mL/hr.
• For a prescription of 0.75 g with 250 mg tablets available, administer 3 tablets.
• To administer 1.2 g of amoxicillin with a concentration of 400 mg per 5 mL, the nurse should administer 15 mL.
• With drug order is 0.3 g and a supply of 100 mg capsules, the nurse should administer 3 capsules.
• To convert 30 mL to tablespoons, the equivalent is 2 tbsp.
• For a child weighing 44 lbs with an order of 5 mg/kg and a medication concentration of 50 mg per mL, the nurse should administer 2 mL.
• To convert 2.5 L to mL, the equivalent is 2,500 mL.
• To administer 125 mcg of digoxin when the supply is 0.25 mg per tablet, the nurse should administer 0.5 tablet.
• To convert 3 tsp to mL, the equivalent is 15 mL.

IV Flow Rate & Infusion Time

• For 1,000 mL of NS over 8 hours, the IV flow rate is 125 mL/hr.
• To administer 1 L of D5NS over 5 hours, the flow rate is 200 mL/hr.
• An IV running at 30 gtt/min with a drop factor of 15 gtt/mL has a flow rate of 120 mL/hr.
• To infuse 50 mL of an antibiotic over 30 minutes using a pump, the IV rate is 100 mL/hr.
• When a patient is receiving 200 mL/hr of NS, a 1 L bag will last 5 hours.
• To administer 400 mg of medication in 250 mL of NS over 2 hours, the infusion rate is 125 mL/hr.
• For 500 mL of LR to infuse at 75 mL/hr, the infusion will take 7 hours to complete.
• To administer 1,000 mL of D5W over 10 hours, the flow rate is 100 mL/hr.
• For 75 mg of a drug in 100 mL NS over 45 minutes, the IV rate is 133 mL/hr.
• A medication order of 250 mL over 2 hours will result in a rate of 125 mL/hr.

Pediatric & Safe Dosage Calculations

• For a child weighing 22 lbs with an order of 15 mg/kg/day divided BID, the dose per administration is 37.5 mg.
• A child prescribed 40 mg/kg of acetaminophen and weighs 18 kg should be given 720 mg.
• If a newborn weighs 3.2 kg and is prescribed 5 mg/kg of a drug, the newborn should be given 16 mg.
• For is 0.5 mg/kg per dose and the and the child weighs 30 kg, the total dose is 15 mg.
• If a child is ordered 20 mg/kg/day divided TID and weighs 15 kg, 100 mg per dose is needed.

Insulin & Heparin Calculations

• For a patient weighing 70 kg with an order of 5 units/kg of heparin, 350 units should be given.
• If a patient weighs 60 kg and is prescribed 8 units/kg of insulin, 480 units should be given.

Titration Calculations

• A heparin drip is ordered at 18 units/kg/hr for a patient weighing 75 kg, the IV bag has 25,000 units in 500 mL.
  • The mL/hr rate is 27 mL/hr.
• A patient is ordered dopamine at 5 mcg/kg/min, and weighs 80 kg, and has an IV bag containing 400 mg in 250 mL.
  • The mL/hr is 15 mL/hr.
• The order is for norepinephrine at 8 mcg/min with concentration of 4 mg in 250 mL
  • Calculate mL/hr is 30 mL/hr.
• A patient needing an insulin drip has 100 units in 250 mL running at 4 units/hr.
  • The mL/hr rate 10 mL/hr.
• Nitroglycerin is ordered at 10 mcg/min, the IV bag has 50 mg in 250 mL of solution
• The mL/hr is 3 mL/hr.

Rounding Rules

• The medication order is 4.267 mL, it should be rounded to 4.3 mL.
• For 1.578 g of medication, available in 0.1 g increments, round to 1.6 g.
• For a prescription is 2.745 mg of medication where 2.5 mg or 3 mg tablets are available, use a 3 mg tablet.
• If IV rate is calculated as 87.56 mL/hr, round to 88 mL/hr.
• The child's dose is calculated as 3.248 mL in an oral syringe needs to be rounded to 3.25 mL.

Safe Dose Range Calculations

• A drug is prescribed at 10 mg/kg/day in two divided doses for a 30 kg child.

• If the safe range is 5-15 mg/kg/day, the dose is safe.

• A patient is ordered 500 mg of a drug with a safe range is 5-10 mg/kg/day and weighs 70 kg.

• This is a safe dose.

• A medication is ordered at 2 mg/kg/day for a 50 kg patient, the safe range is 100-150 mg/day

  • This is a safe dose.

• A pediatric dose is 7 mg/kg/day and the child weighs 18 kg, and you know the safe range is 5-8 mg/kg/day.

  • This is a safe dose.

• The max daily acetaminophen dose is 75 mg/kg/day.

  • A 20 kg child receives 1,000 mg every 6 hours: This exceeds the safe limit.