NCLEX Dosage Calculation Practice: Formulas and Examples
6 min read · Updated
Dosage questions on the NCLEX-RN usually ask you to type a number, and the on-screen calculator is available. What trips people up is not the arithmetic but units and rounding, so convert first and read exactly how the question wants the answer recorded.
The formulas
| Problem | Formula |
|---|---|
| Tablets or liquid | (Desired dose / dose on hand) x quantity |
| Weight-based dose | mg/kg x weight in kg |
| IV rate by pump | Total volume (mL) / time (hours) = mL/hour |
| Dose-based infusion | Dose per hour / concentration (per mL) = mL/hour |
| Gravity drip rate | (Volume in mL x drop factor) / time in minutes = gtt/min |
Rules that save points
- Convert to the same units before you calculate: 1 g = 1,000 mg, 1 mg = 1,000 mcg, 1 kg = 2.2 lb.
- Round only at the end, and only as the question says: whole number or nearest tenth.
- Ask whether the answer makes sense: 30 tablets or 400 mL/hour of heparin should make you check your setup.
Worked examples
A child who weighs 44 lb has a prescription for amoxicillin 25 mg/kg/day divided into two doses. How many milligrams should the nurse give per dose?
- A250 mg
- B500 mg
- C550 mg
- D1,100 mg
Explanation
44 lb / 2.2 = 20 kg. 25 mg/kg/day x 20 kg = 500 mg per day. Divided into two doses: 250 mg per dose. 500 mg is the daily total and 550 mg comes from using pounds instead of kilograms.
1,000 mL of lactated Ringer's is to infuse over 8 hours. At how many mL/hour should the nurse set the pump?
- A80 mL/hour
- B125 mL/hour
- C150 mL/hour
- D167 mL/hour
Explanation
1,000 mL / 8 hours = 125 mL/hour.
More practice
Each full-length exam includes calculation items you type yourself, marked the way the question asks you to round.