The 5-Step Method (Use This Every Time)

Almost every dosage problem is solved the same way. Memorize these five steps and apply them to all the problems below.

Read & label what you have. Find the D (desired/ordered dose), the H (strength you have on hand), and the Q (the form the “have” comes in — 1 tablet, or the mL the strength is stated per). For IVs, find the volume, time, and drop factor.
Match the units. If D and H are in different units (g vs. mg, mcg vs. mg, lb vs. kg), convert one first so they match. This is where most errors happen.
Set up the formula. Use D / H × Q for a dose, or the IV formula for a rate. Write the units next to every number.
Solve. Divide D by H, then multiply by Q. Do the arithmetic carefully.
Check & round. Is only the right unit left? Is the answer reasonable? Round per the rule (tablets = whole/half if scored; liquids = tenth; gtt/min and mL/hr = whole number).

Dose: X = Desired (D) Have (H) × Quantity (Q)

Source: ATI Dosage Calculation; Lippincott.

Part 1 — Conversions

Rule to remember: the metric ladder is kg → g → mg → mcg, each step ×1000. Going to a smaller unit, multiply (move the decimal right 3 places). Going to a larger unit, divide (move the decimal left 3 places).

Problem 1. Convert 2.5 g to milligrams.

How to work it out:

Grams → milligrams is going from a larger unit to a smaller one, so you multiply.
Each step down the ladder is ×1000.
2.5 × 1000 = 2500. (Move the decimal 3 places right: 2.5 → 2500.)

Answer: 2500 mg.

Problem 2. Convert 750 mcg to milligrams.

How to work it out:

Micrograms → milligrams is going from a smaller unit to a larger one, so you divide.
750 ÷ 1000 = 0.75. (Move the decimal 3 places left: 750 → 0.75.)
Add the leading zero: 0.75, not .75.

Answer: 0.75 mg.

Problem 3. A patient weighs 165 lb. Convert to kilograms.

How to work it out:

The equivalent is 1 kg = 2.2 lb.
To go from pounds to kilograms, divide by 2.2.
165 ÷ 2.2 = 75.

Answer: 75 kg.

Problem 4. Convert 0.75 L to milliliters.

How to work it out:

1 L = 1000 mL. Liters → mL goes to a smaller unit, so multiply.
0.75 × 1000 = 750.

Answer: 750 mL.

Problem 5. A child drinks 3 oz of juice. How many mL (1 oz = 30 mL)?

How to work it out:

Each ounce is 30 mL.
Multiply the number of ounces by 30: 3 × 30 = 90.

Answer: 90 mL.

Part 2 — Oral Medications

Problem 6. Order: 1 g. Available: 500 mg tablets. How many tablets?

How to work it out:

Label: D = 1 g, H = 500 mg, Q = 1 tablet.
Match units: D is in grams, H in mg — convert 1 g = 1000 mg.
Set up: (1000 mg ÷ 500 mg) × 1 tablet.
Solve: 1000 ÷ 500 = 2, × 1 = 2.
Check: 2 tablets is reasonable.

Answer: 2 tablets.

Problem 7. Order: 0.25 mg. Available: 0.125 mg tablets. How many tablets?

How to work it out:

Label: D = 0.25 mg, H = 0.125 mg, Q = 1 tablet. Units already match.
Set up: (0.25 ÷ 0.125) × 1.
Solve: 0.25 ÷ 0.125 = 2.
Check: the order is double the tablet strength, so 2 tablets makes sense.

Answer: 2 tablets.

Problem 8. Order: 60 mg. Available: 40 mg scored tablets. How many tablets?

How to work it out:

Label: D = 60 mg, H = 40 mg, Q = 1 tablet.
Set up: (60 ÷ 40) × 1.
Solve: 60 ÷ 40 = 1.5.
Check the form rule: a half tablet is only allowed because the tablet is scored.

Answer: 1.5 tablets.

Problem 9. Order: 375 mg. Available: 250 mg / 5 mL (liquid). How many mL?

How to work it out:

Label: D = 375 mg, H = 250 mg, Q = 5 mL (the volume the strength comes in).
Set up: (375 ÷ 250) × 5 mL.
Solve: 375 ÷ 250 = 1.5, × 5 = 7.5.
Check: use an oral syringe; round to the tenth.

Answer: 7.5 mL.

Problem 10. Order: 0.5 g. Available: 125 mg / 5 mL. How many mL?

How to work it out:

Label: D = 0.5 g, H = 125 mg, Q = 5 mL.
Match units: convert 0.5 g = 500 mg.
Set up: (500 ÷ 125) × 5.
Solve: 500 ÷ 125 = 4, × 5 = 20.

Answer: 20 mL.

Part 3 — Injectable Medications

Problem 11. Order: 60 mg. Available: 80 mg / mL. How many mL?

How to work it out:

Label: D = 60 mg, H = 80 mg, Q = 1 mL.
Set up: (60 ÷ 80) × 1.
Solve: 60 ÷ 80 = 0.75.
Check: under 1 mL → use a tuberculin syringe; round to the hundredth.

Answer: 0.75 mL.

Problem 12. Order: 0.5 mg. Available: 250 mcg / mL. How many mL?

How to work it out:

Label: D = 0.5 mg, H = 250 mcg, Q = 1 mL.
Match units: convert 0.5 mg = 500 mcg (mg→mcg, multiply by 1000).
Set up: (500 ÷ 250) × 1.
Solve: 500 ÷ 250 = 2.

Answer: 2 mL.

Problem 13. A reconstituted vial reads 1 g / 4 mL. Order: 250 mg. How many mL?

How to work it out:

Use the reconstituted concentration as H: H = 1 g / 4 mL, so Q = 4 mL.
Match units: convert 1 g = 1000 mg. So H = 1000 mg per 4 mL.
Set up: (250 ÷ 1000) × 4.
Solve: 250 ÷ 1000 = 0.25, × 4 = 1.

Answer: 1 mL.

Problem 14. Order: heparin 5000 units subQ. Available: 10,000 units / mL. How many mL?

How to work it out:

Label: D = 5000 units, H = 10,000 units, Q = 1 mL. Units match (both in “units”).
Set up: (5000 ÷ 10,000) × 1.
Solve: 5000 ÷ 10,000 = 0.5.
Safety: heparin is high-alert — independent double-check with a second nurse.

Answer: 0.5 mL.

Problem 15. Order: 15 units of regular insulin subQ. How is it measured?

How to work it out:

Insulin is dosed in units and drawn up in an insulin syringe that matches the vial (U-100).
With the right syringe you do not calculate a volume — you draw to the ordered unit mark.
Draw to the 15-unit mark; double-check with a second nurse.

Answer: draw to the 15-unit mark on an insulin syringe.

Part 4 — IV Calculations

Formulas: pump rate mL/hr = volume ÷ time (hr); drip rate gtt/min = (volume × drop factor) ÷ time (min); infusion time = volume ÷ rate.

Problem 16. Infuse 1000 mL over 6 hours on a pump. Rate in mL/hr?

How to work it out:

Pump rate uses volume ÷ time in hours.
1000 mL ÷ 6 hr = 166.67.
Round pump rates to a whole number: 167.

Answer: 167 mL/hr.

Problem 17. Infuse 250 mL over 2 hours with 15 gtt/mL tubing. Rate in gtt/min?

How to work it out:

gtt/min needs time in minutes — convert 2 hr × 60 = 120 min.
Set up: (250 mL × 15 gtt/mL) ÷ 120 min.
Solve: 250 × 15 = 3750; 3750 ÷ 120 = 31.25.
Round drops to a whole number: 31.

Answer: ≈ 31 gtt/min.

Problem 18. Order 100 mL/hr with microdrip (60 gtt/mL) tubing. Rate in gtt/min?

How to work it out:

With microdrip (60 gtt/mL), the 60 in the formula cancels the 60 minutes in an hour.
So gtt/min equals mL/hr — the numbers are the same.
100 mL/hr → 100 gtt/min.

Answer: 100 gtt/min.

Problem 19. A 500 mL bag is infusing at 125 mL/hr. How long will it take?

How to work it out:

Infusion time = volume ÷ rate.
500 mL ÷ 125 mL/hr = 4.

Answer: 4 hours.

Problem 20. A 50 mL antibiotic piggyback is ordered over 30 minutes on a pump. Rate in mL/hr?

How to work it out:

The pump needs an hourly rate — convert 30 min = 0.5 hr.
Set up: 50 mL ÷ 0.5 hr.
Solve: 50 ÷ 0.5 = 100.
Sense check: giving 50 mL in half an hour is 100 mL in a full hour — correct.

Answer: 100 mL/hr.

Part 5 — Challenge (Weight-Based, Multi-Step)

Problem 21. Order: 10 mg/kg. The child weighs 44 lb. How many mg per dose?

How to work it out:

Convert weight first: 44 lb ÷ 2.2 = 20 kg.
Multiply by the per-kg dose: 20 kg × 10 mg/kg = 200.
The “kg” cancels, leaving mg.

Answer: 200 mg.

Problem 22. Using the 200 mg dose from #21, the supply is 250 mg / 5 mL. How many mL?

How to work it out:

Label: D = 200 mg, H = 250 mg, Q = 5 mL.
Set up: (200 ÷ 250) × 5.
Solve: 200 ÷ 250 = 0.8, × 5 = 4.

Answer: 4 mL.

Problem 23. Order: 5 mg/kg/day divided into 2 doses for a 22 lb child. How many mg per dose?

How to work it out:

Convert weight: 22 lb ÷ 2.2 = 10 kg.
Daily dose: 10 kg × 5 mg/kg = 50 mg per day.
Divide by the number of doses: 50 ÷ 2 = 25.
(Careful: the question asks per dose, not per day.)

Answer: 25 mg per dose.

Problem 24. Infuse 1000 mL over 8 hours with 20 gtt/mL tubing. Rate in gtt/min?

How to work it out:

Convert time: 8 hr × 60 = 480 min.
Set up: (1000 × 20) ÷ 480.
Solve: 1000 × 20 = 20,000; 20,000 ÷ 480 = 41.67.
Round to a whole number: 42.

Answer: ≈ 42 gtt/min.

Problem 25. Order: 0.125 mg. Available: 0.25 mg scored tablets. How many tablets?

How to work it out:

Label: D = 0.125 mg, H = 0.25 mg, Q = 1 tablet. Units match.
Set up: (0.125 ÷ 0.25) × 1.
Solve: 0.125 ÷ 0.25 = 0.5.
Form rule: the tablet is scored, so a half tablet is allowed.

Answer: ½ (0.5) tablet.

Where Students Go Wrong (and How to Avoid It)

Skipping the conversion. If D and H units differ, convert before plugging into the formula (Problems 6, 10, 12, 13).
Leaving time in hours for gtt/min. Always change hours to minutes first (Problems 17, 24).
Wrong rounding. Tablets are whole (or half if scored); liquids to the tenth; gtt/min and mL/hr to a whole number.
Forcing a volume for insulin. Insulin is drawn to the unit mark, not calculated (Problem 15).
Ignoring an unreasonable answer. Many tablets, a huge volume, or an extreme rate = recheck the units and the decimal.

APA Reference List

Assessment Technologies Institute. (2023). Dosage calculation and safe medication administration. ATI Nursing Education.

Institute for Safe Medication Practices. (2024). Safe dosage calculation and high-alert medication practices. https://www.ismp.org

Karch, A. M. (2023). Focus on nursing pharmacology (9th ed.). Wolters Kluwer / Lippincott.

National Council of State Boards of Nursing. (2023). NCLEX-RN examination test plan. https://www.ncsbn.org

Note: Rounding rules vary by textbook and facility; always follow your program’s standards and verify high-alert calculations. Content reflects U.S. nursing practice and NCLEX standards current as of 2026.

Practice Problems

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Welcome & Getting Started

Launch RN Simulator

Wellness Center

Nursing Foundations

Fundamentals & Safety

Pharmacology

Dosage Calculations

Leadership, Management & Delegation

Medical-Surgical Body Systems

Neurological System

Sensory System

Endocrine System

Respiratory System

Cardiovascular System

Hematologic/Immune/Lymphatic System

Gastrointestinal (GI) System

Renal & Genitourinary

Reproductive System

Musculoskeletal System

Integumentary System

Specialty Areas

Maternity

Infectious Diseases

Pediatrics

Mental Health

NCLEX Success Center

Clinical Judgment Practice

Prioritization Practice

Delegation Practice

Lab Values

Final Review