ATI Dosage Calculation: Topics, Methods, and Worked Examples
Shows the work. Every example is computed with the formula and numbered steps. For study and exam practice, not for patient care.
Some nursing programs assign ATI’s Dosage Calculation and Safe Medication Administration program for med math. This page summarizes what ATI’s public page for educators says the program covers, then works one problem for each topic. It doesn’t reproduce ATI’s content or questions.
What ATI says the program includes
ATI describes it as an online study program of tutorials, learning activities, case studies, and assessments. According to that page:
- Modules: Case Studies, Critical Care Medications, Dosage by Weight, Injectable Medication, Medication Administration, Oral Medication, Parenteral (IV) Medications, Pediatric Medications, Powdered Medication, and Safe Medication Administration.
- Three calculation methods: Ratio and Proportion, Dimensional Analysis, and Desired Over Have.
- Assessments: they work alongside the modules, with three forms per proctored assessment, each of 20 questions plus five pretest questions.
Your program decides which modules you take, when the proctored assessment is given, and what score it requires; ask your instructor.
One worked example per topic
Each example is solved step by step with the method this site uses (Desired over Have, or the matching formula). Any of the three methods gives the same answer.
Oral medication, with a unit conversion
Order: clonidine 100 mcg PO twice daily. Available: clonidine 0.05 mg tablets. How many tablets?
- Desired dose
- 0.1 mg
- Have
- 0.05 mg
- Give as
- Tablets
- Scored tablet
- Yes
Formula Amount = desired ÷ have × vehicle.
- Tablets = desired dose ÷ tablet strength.
- 0.1 mg ÷ 0.05 mg = 2 tablets.
- The answer is a whole number of tablets: 2 tablets.
Answer 2 tablets
Injectable medication
Order: enoxaparin 40 mg subcut daily. Available: enoxaparin 300 mg/3 mL multiple-dose vial. How many mL?
- Desired dose
- 40 mg
- Have
- 300 mg
- Vehicle
- 3 mL
- Give as
- mL (liquid or injection)
Formula Amount = desired ÷ have × vehicle.
- mL = desired ÷ have × vehicle.
- 40 mg ÷ 300 mg × 3 mL = 0.4 mL.
- 0.4 mL is exact, so no rounding is needed.
Answer 0.4 mL
Dosage by weight
Order: azithromycin 5 mg/kg/dose PO daily. The client weighs 53 kg. Available: azithromycin oral suspension 200 mg/5 mL. How many 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
Powdered medication
Order: ceftriaxone 250 mg IM once. Available: ceftriaxone 500 mg vial. The label says: for IM use, add 1 mL of diluent to yield 350 mg/mL. How many mL?
- Solve for
- Volume to give (mL)
- Vial amount
- 500 mg
- Diluent added
- 1 mL
- Concentration after mixing
- 350 mg/mL
- Ordered dose
- 250 mg
Formula mL = ordered dose ÷ concentration after mixing.
- Adding 1 mL to the 500 mg vial gives 350 mg/mL (from the label).
- mL = ordered dose ÷ concentration.
- 250 mg ÷ 350 mg/mL = 0.7143 mL.
- 0.714286 mL is less than 1 mL, so round to the nearest hundredth: 0.71 mL.
Answer 0.71 mL
Parenteral (IV) medication
Order: magnesium sulfate 4 g in 100 mL IV over 60 minutes by infusion pump. At how many mL/hr?
- Solve for
- Pump rate (mL/hr)
- Volume
- 100 mL
- Infusion time
- 60 minutes
Formula mL/hr = total volume ÷ total hours.
- Convert minutes to hours: 60 ÷ 60 = 1 hour.
- mL/hr = 100 mL ÷ 1 hour = 100 mL/hr.
- 100 mL/hr is exact, so no rounding is needed.
Answer 100 mL/hr
Critical care medication
Order: dobutamine 20 mcg/kg/min IV. Available: dobutamine 500 mg in 250 mL. The client weighs 102 kg. At how many mL/hr?
- Solve for
- Pump rate (mL/hr)
- Ordered dose
- 20 mcg/kg/min
- Weight
- 102 kg
- Drug in the bag
- 500 mg
- Bag volume
- 250 mL
Formula mL/hr = mcg/kg/min × kg × 60 ÷ mcg per mL.
- Concentration = 500,000 mcg ÷ 250 mL = 2,000 mcg/mL.
- Dose per hour = 20 mcg/kg/min × 102 kg × 60 min/hr = 122,400 mcg/hr.
- mL/hr = 122,400 mcg/hr ÷ 2,000 mcg/mL = 61.2 mL/hr.
- 61.2 mL/hr is exact, so no rounding is needed.
Answer 61.2 mL/hr
How to prepare
- Pick the method your course teaches and use it on every problem, including the conversions.
- Convert units and weights first; most wrong answers start with a unit.
- Round only as the question tells you, and write a leading zero before any decimal.
- Work the practice problems or a worksheet, and use the calculators to check: each shows the formula and every step.
ATI is a trademark of Assessment Technologies Institute. DoseRightRN is independent: it is not affiliated with, endorsed by, or sponsored by the exam's owner, and uses the exam's name only to describe what the page covers.
Sources
- Dosage Calculation and Safe Medication Administration — ATI (Assessment Technologies Institute)
- NCLEX-RN Test Plan, effective April 2026 — National Council of State Boards of Nursing (NCSBN)
- Clinical Calculations: With Applications to General and Specialty Areas — Elsevier (Kee, Marshall, et al.)
- Calculate with Confidence — Elsevier (Morris)