HESI Dosage Calculation and Math: What to Study

HESI is Elsevier’s family of nursing exams. Elsevier’s public pages describe several of them, including the Admission Assessment (A2) Exam, Specialty Exams, and the Exit Exam. Math shows up at two ends of a nursing program: basic math on the admission exam, and dosage calculation as part of NCLEX readiness on the Exit Exam. This page describes both from Elsevier’s public pages, without reproducing HESI content.

HESI A2: math before nursing school

Elsevier’s own review guide for the A2, Admission Assessment Exam Review, lists Mathematics as the first of its subject chapters, alongside reading comprehension, vocabulary, grammar, biology, chemistry, and anatomy and physiology. Your school chooses which sections it gives and what score it requires, so check with the program you’re applying to.

Dosage calculation builds on the same skills: fractions and decimals, ratios and proportions, and conversions between units. These worked conversions use exactly those.

Household measure to mL

A client is told to take 1.5 cups of an oral liquid. Use 1 cup = 240 mL. How many mL is this?

Value

1.5 cup

To

mL

Formula Multiply or divide by the conversion factor.

1. 1 cup = 240 mL.
2. 1.5 cups × 240 mL = 360 mL.
3. 360 mL is exact, so no rounding is needed.

Answer 360 mL

Pounds to kilograms

A client weighs 121 lb. Use 1 kg = 2.2 lb. What is the weight in kg?

Value

121 lb

To

kg

Formula Multiply or divide by the conversion factor.

1. kg = lb ÷ 2.2.
2. 121 ÷ 2.2 = 55 kg.
3. 55 kg is exact, so no rounding is needed.

Answer 55 kg

Milligrams to grams

Order: allopurinol 100 mg PO. How many g is this dose?

Value

100 mg

To

g

Formula Multiply or divide by the conversion factor.

1. 1 g = 1,000 mg, so divide by 1,000.
2. 100 ÷ 1,000 = 0.1 g.
3. 0.1 g is exact, so no rounding is needed.

Answer 0.1 g

The conversion charts list common amounts for each pair.

HESI Exit Exam: dosage calculation as NCLEX readiness

Elsevier says the Exit Exam measures readiness for the NCLEX with an exam blueprint that matches the current NCLEX test plan. In the 2026 NCLEX-RN test plan, dosage calculation belongs to Pharmacological and Parenteral Therapies, so expect medication math in that context: oral and injectable doses, IV rates, and weight-based doses.

IV infusion by dose per hour

Order: magnesium sulfate 1.5 g/hr IV. Available: magnesium sulfate 20 g in 500 mL. At how many mL/hr should the pump be set?

Solve for

Pump rate (mL/hr)

Ordered dose per hour

1.5 g/hr

Drug in the bag

20 g

Bag volume

500 mL

Formula mL/hr = ordered units/hr ÷ units per mL.

1. Concentration = 20 g ÷ 500 mL = 0.04 g/mL.
2. mL/hr = 1.5 g/hr ÷ 0.04 g/mL = 37.5 mL/hr.
3. 37.5 mL/hr is exact, so no rounding is needed.

Answer 37.5 mL/hr

Weight-based oral dose

Order: digoxin 11.3 mcg/kg/day PO divided every 12 hours. The child weighs 27.3 kg. Available: digoxin oral solution 0.05 mg/mL. How many mL per dose?

Solve for

Dose from mg/kg

Weight

27.3 kg

Doses per day

2

Ordered dose per kg

11.3 mcg/kg/day

Have

0.05 mg

Vehicle

1 mL

Formula Dose = mg/kg × weight in kg.

1. Daily dose = 11.3 mcg/kg/day × 27.3 kg = 308.49 mcg/day.
2. Divided every 12 hours is 2 doses a day: 308.49 ÷ 2 = 154.245 mcg per dose.
3. mL = 0.1542 mg ÷ 0.05 mg × 1 mL = 3.0849 mL.
4. Round to the nearest hundredth: 3.08 mL.

Answer 3.08 mL

How to prepare

• For the A2, practice fractions, decimals, and conversions until they are quick without a calculator, then check with one.
• For the Exit Exam, study dosage calculation the way you would for the NCLEX: see the NCLEX page and the general dosage calculation exam guide.

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