Nursing care
Dosage calculation practice problems with worked answers and the error behind each
Written and reviewed by Nicole Ramirez, BSN, RN, CMSRN · 5 min read · Updated November 2026
Short answer
These dosage calculation practice problems cover six common types: tablets, oral liquids, weight-based doses, safe dose ranges, IV pump rates in mL/hr and gravity drip rates in drops per minute. Each shows the setup with units carried through, the answer, and the mistake that most often produces a wrong result. All numbers are practice figures, not real orders.
Rules to apply before you start
Every problem here uses dimensional analysis or the equivalent dose ordered divided by dose on hand times quantity. Set up units so they cancel, and if the unit left over is not the one you need, the setup is wrong before you touch the calculator. Do not round partway through; round only the final answer.
| Situation | Rule |
|---|---|
| Liquid dose over 1 mL | Round to the tenth |
| Liquid dose under 1 mL | Round to the hundredth |
| Drops per minute | Round to the nearest whole drop |
| Writing decimals | Use a leading zero (0.5 mg) and no trailing zero (5 mg, not 5.0 mg) |
| Weight conversion | 1 kg = 2.2 lb |
Your program or facility may set different rounding rules, and the exam question's instructions override any general rule. Read the last line of the stem for the unit and the rounding instruction before you start working.
Oral doses: tablets and liquids
Tablet and liquid problems test whether you can match the ordered dose to what is on the label. The most frequent error is reading the label's total amount instead of its concentration, for example treating 250 mg per 5 mL as 250 mg per mL.
Worked example
- Write the order: 0.5 mg
- Divide by strength: 0.5 mg / 0.25 mg per tablet
- mg cancels, leaving tablets
Worked example
- Concentration fraction: 5 mL / 250 mg
- Multiply by 375 mg; mg cancels
- 5 x 375 = 1875; 1875 / 250 = 7.5
Weight-based doses and safe dose range
Weight-based problems add a conversion step, and the classic mistake is multiplying mg/kg by the weight in pounds, which gives a dose 2.2 times too large. Convert first, then check the result against the safe range before you prepare anything.
Worked example
- Convert: 33 lb / 2.2 = 15 kg
- Dose: 15 mg/kg x 15 kg = 225 mg
- Volume: 225 mg x 5 mL / 160 mg = 7.03 mL
- Round to the tenth: 7.0, written as 7 mL
Worked example
- Low end: 10 x 15 = 150 mg
- High end: 15 x 15 = 225 mg
- Compare: 200 mg falls between 150 and 225 mg
Open RN uses the same three-step routine: calculate both ends of the range, then compare the ordered dose. A dose above the range is a hold-and-clarify finding, never something to adjust yourself.
IV rates: pump and gravity
Pump problems ask for mL/hr; gravity problems ask for drops per minute and need the tubing's drop factor, which is printed on the package. Macrodrip sets deliver 10, 15 or 20 drops per mL and microdrip sets deliver 60.
Worked example
- 1,000 mL / 8 hr
- = 125 mL/hr
Worked example
- Numerator: 500 x 15 = 7,500 gtt
- Denominator: 4 x 60 = 240 min
- 7,500 / 240 = 31.25
- Round to a whole drop
Sources and further reading
Open RN Nursing Skills: Rounding. Round only the final answer; tenths over 1 mL, hundredths under 1 mL; whole drops; leading zero and no trailing zero.
Open RN Nursing Skills: Weight-Based Calculations. 1 kg = 2.2 lb and the dimensional analysis setup for mg/kg liquid doses.
Open RN Nursing Skills: Safe Dosage Range. Calculating low and high ends of a safe range and comparing the ordered dose.
Open RN Nursing Skills: IV Infusion by Gravity. Drip rate formula, macrodrip 10, 15 or 20 gtt/mL and microdrip 60 gtt/mL, rounding drops to whole numbers.
The next step on this is the same as on everything else here: answer questions and read the rationales. Our dosage calculation and lab values practice questions are the closest set to what this page covers.
Common questions
Where can I practice dosage calculations?
Work problems by hand using real labels from your skills lab, then check against a worked key. Open RN's free Nursing Skills textbook has a math calculations chapter with practice items. Redo every missed problem a day later without looking at the answer.
What are common dosage calculation questions in nursing school?
Tablets, oral liquids, reconstituted medications, weight-based pediatric doses, safe dose range checks, IV pump rates, gravity drip rates and infusion completion times. Multi-step problems combine a weight conversion with a concentration in one question.
Should I use dimensional analysis or the formula method?
Either gives the same answer when set up correctly. Dimensional analysis is easier to check because the units must cancel to the one you want, which catches setup errors in multi-step and weight-based problems.
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