NCLEX-RN cheat sheet · Pharmacology
Dosage calculation
Equivalents, rounding, dimensional analysis, weight-based doses, IV rates, titration and NCSBN's calculation rules
AI-checkedChecked by AI against current guidelines, with spot-checks by a registered nurse.
Most dosage math comes down to a few equivalents and one reliable method. Calculation errors are medication errors, so double-check every one.
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At a glance
Equivalents to memorize
| This | Equals |
|---|---|
| 1 teaspoon | 5 mL |
| 1 tablespoon | 3 teaspoons, or 15 mL |
| 1 ounce | 30 mL |
| 1 cup | 8 ounces, or 240 mL |
| 1 kg | 1000 g, and 2.2 lb |
| 1 g | 1000 mg |
| 1 mg | 1000 mcg |
| 1 L | 1000 mL |
Moving the decimal: Metric units step by tens: to a smaller unit, the decimal moves right; to a larger unit, left. 0.1 mg is 100 mcg; 500 mg is 0.5 g.
Units, percent, ratios and time
- Insulin and heparin are measured in units; insulin syringes are marked in units.
- A percent is grams per 100 mL: 5% dextrose has 5 g in every 100 mL. 0.9% saline has 9 g of salt in 1000 mL.
- A 1 to 1000 ratio, like some epinephrine: 1 g in 1000 mL, or 1 mg per mL.
- 24-hour clock: from 1 AM to noon, drop the colon (6:30 AM is 0630); from 1 PM, add 1200 (2:45 PM is 1445). 12:30 AM is 0030; 12:30 PM is 1230.
- Oral syringes are more precise than cups for small doses, especially for children.
Dimensional analysis
- 1. Write the goal unit, like mL or tablets.
- 2. Start with a fraction that has the goal unit on top, like 5 mL per 125 mg.
- 3. Add fractions so each unwanted unit appears once on top and once on the bottom, and cancels.
- 4. Multiply across the tops, multiply across the bottoms, then divide.
- Units left aren't the goal unit? The setup is wrong: fix it before you calculate.
Rounding, leading and trailing zeros
- Round only at the end. Rounding early adds error.
- A common convention: adult liquid doses over 1 mL to the tenth (2.36 mL is 2.4); doses under 1 mL, and children's doses, to the hundredth (0.276 is 0.28). Drops: whole numbers. Follow your agency's policy.
- Look one place past the one you keep: 5 or more rounds up, under 5 rounds down.
- A leading zero (0.6 mg), but never a trailing zero: 6.0 can be misread as 60.
Oral and weight-based doses: worked examples
| Problem | Work | Answer |
|---|---|---|
| Order 50 mg; tablets are 25 mg | 50 ÷ 25 | 2 tablets |
| Order 0.1 mg; tablets are 50 mcg | Convert first: 0.1 mg is 100 mcg. 100 ÷ 50 | 2 tablets |
| Order 250 mg; liquid is 125 mg per 5 mL | 250 ÷ 125 is 2; 2 × 5 mL | 10 mL |
| Powder: after mixing, 200 mg per mL; order 300 mg | Use the concentration after mixing, not the diluent volume | 1.5 mL |
| Child 33 lb; order 10 mg per kg; liquid 100 mg per 5 mL | Kilograms first: 33 ÷ 2.2 is 15 kg. 10 × 15 is 150 mg. 150 ÷ 100 × 5 | 7.5 mL |
| Infant 3.6 kg; order 0.5 mg per kg; supply 10 mg per mL | 0.5 × 3.6 is 1.8 mg. 1.8 ÷ 10 | 0.18 mL, in a small syringe |
Safe dosage range
- Before giving a weight-based dose, check the safe range in a drug reference. Multiply the weight by the low limit and by the high limit: the order must fall between them.
- Example: an infant weighs 8 kg; the safe range is 10 to 15 mg per kg per dose, so 80 to 120 mg. The order is 150 mg: too high. Hold it and clarify the order.
- Does it make sense? 20 tablets for one dose means stop and recheck.
Titration
- The order sets the limits: the starting dose, how much to change it, how often, the target, and the maximum.
- Before each change, assess against the target; after it, reassess, and document both.
- Never go beyond the maximum, change it faster than ordered, or titrate without assessing. Target not reached at the maximum, or the client worsens: call the provider.
IV rates: formulas and worked examples
| To find | Use | Example |
|---|---|---|
| mL per hour (pump) | Total volume ÷ hours. Minutes? ÷ minutes × 60 | 1,000 mL over 8 hours: 125 mL an hour. 50 mL over 30 minutes: 50 ÷ 30 × 60 = 100 mL an hour |
| Drops per minute (gravity) | Volume × drop factor ÷ minutes | 1,000 mL over 8 hours, 15 drops per mL: 15,000 drops ÷ 480 minutes = 31.25, so 31 drops a minute |
| Hours to finish | Volume ÷ rate. Decimal hour × 60 = minutes | 1,000 mL at 80 mL per hour: 12.5 hours; 0.5 hour is 30 minutes. Started at 0700, it ends at 1930 |
| Units per hour to mL per hour | Units per hour ÷ units per mL | Heparin 25,000 units in 500 mL is 50 units per mL; 1,200 units an hour ÷ 50 = 24 mL an hour |
Drop factors: Macrodrip: 10, 12, 15 or 20 drops per mL. Microdrip: 60, so drops per minute equal mL per hour. Round to a whole drop.
Micrograms per kilogram per minute
- Steps: concentration, dose per minute, per hour, then mL per hour.
- 400 mg in 250 mL is 1,600 mcg per mL. 5 mcg per kg per minute × 80 kg is 400 mcg a minute; × 60 is 24,000 mcg an hour; ÷ 1,600 is 15 mL an hour.
- Weight in pounds? Kilograms first: 176 lb ÷ 2.2 is 80 kg. Round the rate as your pump and agency policy allow.
- Check backwards: a pump at 18 mL an hour, at 50 units per mL, delivers 900 units an hour.
On the exam: NCSBN's calculation rules
| Rule | What it means |
|---|---|
| Precision | The item asks for a whole number, or one or two decimal places. Whole number: type 2, not 2.0 |
| Decimal point | When decimals are asked for, type the decimal point, with a leading zero |
| Round only at the end | Child 45 lb; 2.5 mg per kg; 20 mg per mL. Exact: 20.4545 kg, 51.136 mg, 2.5568 mL: enter 2.56. Rounding to 20 kg first gives 2.5 mL: wrong, with no partial credit |
| Your tools | On-screen calculator and noteboard; no handheld calculators or conversion tables. Conversions are in your head |
Priority and safety calls
- ★ A dose outside the safe range: don't give it. Hold it and clarify the order with the prescriber.
- Check the pump's programming against the order and the bag's concentration before you start.
- Heparin and other high-alert drips are double-checked by a second nurse, under agency policy.
How the NCLEX tests it
- Read each item for the unit it wants and how to round; type only the number, in that unit.
- Dose traps: rounding early, forgetting to convert milligrams or pounds, and using the diluent volume.
- IV traps: forgetting minutes to hours, the wrong drop factor, an unconverted decimal hour, skipping milligrams to micrograms.
- Child 18 kg, 15 mg per kg, 160 mg per 5 mL: 270 mg, then 8.4375 mL. For a child, round to the hundredth: 8.44 mL.
- 1,000 mL over 8 hours, 15 drops per mL: 31 drops a minute. 125 is the mL per hour, not the drops.
Practice it next
This sheet comes from Dosage calculation I: conversions and doses and Dosage calculation II: IV rates and titration and NCSBN's calculation rules in our NCLEX-RN course. Try free practice questions, or see the lessons it was written from.
Quick self-quiz
- To convert pounds to kilograms, divide by ___.
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2.2 - 9:05 in the evening is ___.
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2105 - Microdrip tubing gives ___ drops per mL.
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60 - 25 mL to run over 15 minutes: set the pump to ___ mL per hour.
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100 - Heparin 25,000 units in 500 mL, ordered at 1,200 units an hour, runs at ___ mL an hour.
Show answer
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Sources
- Open RN, Nursing Skills 2e, 5.4 Equivalencies
- Open RN, Nursing Skills 2e, 5.12 Safe Dosage Range
- Open RN, Nursing Skills 2e, 5.17 Multi-Step Calculations
- NCSBN, 2026 NCLEX Candidate Bulletin (on-screen calculator)
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Educational use only. This sheet is a study aid for the NCLEX-RN, not a substitute for clinical judgment, your facility’s policy or the provider’s orders. Where practice varies, follow facility policy and state law. NCLEX® and NCLEX-RN® are registered trademarks of NCSBN, which does not endorse these materials.