Dosage calculations, IV flow rates, conversions, and practice drills
Keep these four core formulas handy — they cover the vast majority of clinical dosage calculations.
Dose = (Desired ÷ Available) × Quantity
Example: Order 500mg, have 250mg/5mL → (500÷250)×5 = 10mL
Use when: Calculating liquid medication doses from stock concentration.
mL/hr = Volume (mL) ÷ Time (hrs)
Example: 1000mL over 8hrs → 1000÷8 = 125 mL/hr
Use when: Setting IV pump rates for continuous infusions.
gtt/min = (Volume × Drop Factor) ÷ Time (min)
Example: 500mL × 15gtt/mL ÷ 240min = 31 gtt/min
Use when: Manual IV infusions using gravity drip sets.
Dose = Weight (kg) × Dose per kg
Example: 22kg × 15mg/kg = 330mg, then convert to mL
Use when: Pediatric and weight‑dependent medication dosing.
Work through clinical calculation scenarios — select an answer and submit to see the full solution.
Problem 1
The provider orders amoxicillin 500 mg PO. The pharmacy supplies amoxicillin 250 mg/5 mL. How many mL should the nurse administer?
Problem 2
Order: 1000 mL NS to infuse over 8 hours. What is the mL/hr rate?
Problem 3
Order: 500 mL LR over 4 hours. Drop factor: 15 gtt/mL. Calculate gtt/min.
Problem 4
Order: acetaminophen 15 mg/kg PO for a child weighing 22 kg. Pharmacy supplies 160 mg/5 mL. How many mL?
Problem 5
Order: levothyroxine 0.075 mg PO daily. Available: 25 mcg tablets. How many tablets?
Problem 6
A patient is receiving 20 gtt/min of NS with a drop factor of 10 gtt/mL. What is the mL/hr rate?
Problem 7
Calculate the body surface area (BSA) for a patient who is 165 cm tall and weighs 68 kg. Use the Mosteller formula: BSA = √[(height cm × weight kg) / 3600]. Round to the nearest hundredth.
Problem 8
A child weighs 18 kg. The safe dosage range is 30–50 mg/kg/day divided q8h. The provider orders 350 mg q8h. Is the ordered dose within the safe range?
Problem 9
Order: 500 mL NS to infuse at 75 mL/hr. The infusion starts at 0900. At what time (military time) will the infusion be completed?
Problem 10
A powdered medication label reads: 'Add 4.5 mL NS to yield 500 mg/5 mL.' The provider orders 350 mg IM. How many mL should the nurse administer?
Problem 11
If 250 mg of a drug is in 5 mL of solution, how many mL contain 175 mg? Solve using ratio-proportion.
Problem 12
Order: ceftriaxone 50 mg/kg IV q12h for a child weighing 33 lb. Pharmacy supplies ceftriaxone 1 g/10 mL after reconstitution. How many mL per dose? (Round to the nearest tenth.)
Complete the first 4 problems to unlock the rest
| From | To | Conversion |
|---|---|---|
| 1 kg | lb | 2.2 lb |
| 1 g | mg | 1000 mg |
| 1 mg | mcg | 1000 mcg |
| 1 L | mL | 1000 mL |
| 1 tsp | mL | 5 mL |
| 1 tbsp | mL | 15 mL |
| 1 oz | mL | 30 mL |
| 1 inch | cm | 2.54 cm |