2.2 Measurement & Conversions
Key Takeaways
- Measurement & Conversions is about 14 items (~35%) — the largest subsection of the NEX math section
- Metric prefixes step by powers of ten: kilo- (x1,000), centi- (x0.01), milli- (x0.001), micro- (x0.000001)
- Memorize the household-to-metric bridge: 1 tsp = 5 mL, 1 tbsp = 15 mL, 1 oz = 30 mL, 1 cup = 240 mL, 1 kg = 2.2 lb
- Dimensional analysis (the factor-label method) cancels units step by step until only the target unit remains
- Temperature: F = (C x 9/5) + 32 and C = (F - 32) x 5/9; normal body temperature is 98.6F = 37C
- The dosage formula is Desired / Have x Quantity = amount to give
- Weight-based dosing requires converting pounds to kilograms first (divide by 2.2) before multiplying by the per-kg dose
- A wrong conversion in dosing can be a tenfold or hundredfold error — always verify units cancel correctly
Measurement & Conversions on the NLN NEX
This is the largest subsection of the NEX math section — about 14 items (~35%) — and the most clinically loaded. Expect metric conversions, household-to-metric bridges, temperature conversion, and direct dosage calculations.
The metric system
| Prefix | Symbol | Multiplier | Example |
|---|---|---|---|
| kilo- | k | 1,000 | 1 kg = 1,000 g |
| (base unit) | — | 1 | gram (g), liter (L), meter (m) |
| centi- | c | 0.01 | 1 cm = 0.01 m |
| milli- | m | 0.001 | 1 mL = 0.001 L |
| micro- | mc / mcg | 0.000001 | 1 mcg = 0.000001 g |
- Moving to a smaller unit, multiply (decimal moves right): 2.5 L = 2,500 mL.
- Moving to a larger unit, divide (decimal moves left): 750 mg = 0.75 g.
Use mcg, not the symbol μg, on nursing tests — handwritten μ is mistaken for mg, a thousandfold error.
Essential nursing conversions
These are pure memorization and appear on nearly every NEX form. Note that household equivalents are approximate clinical standards (1 oz = 30 mL, not the precise 29.57 mL).
| Conversion | Value | Category |
|---|---|---|
| 1 kilogram | 2.2 pounds | Weight |
| 1 inch | 2.54 cm | Length |
| 1 teaspoon | 5 mL | Volume |
| 1 tablespoon | 15 mL (3 tsp) | Volume |
| 1 fluid ounce | 30 mL (2 tbsp) | Volume |
| 1 cup | 240 mL (8 oz) | Volume |
| 1 pint | 480 mL (16 oz) | Volume |
| 1 quart | 960 mL (32 oz) | Volume |
| 1 liter | 1,000 mL | Volume |
| 1 gram | 1,000 mg | Weight |
| 1 milligram | 1,000 mcg | Weight |
Trap: to go from kg to lb you multiply by 2.2; to go from lb to kg you divide. Mixing these up produces an answer about 4.8x too large.
IV flow-rate basics also appear here. The drop-rate formula is gtt/min = (volume in mL x drop factor in gtt/mL) / time in minutes. To infuse 1,000 mL over 8 hours with a 15 gtt/mL set: 1,000 x 15 = 15,000, divided by 480 minutes = about 31 gtt/min. The infusion-pump (mL/hr) form is simply total volume divided by total hours: 1,000 mL / 8 hr = 125 mL/hr.
Dimensional analysis (factor-label method)
Write the starting value, then multiply by conversion factors arranged so unwanted units cancel diagonally, leaving only the target unit.
Convert 154 lb to kg: 154 lb x (1 kg / 2.2 lb) = 70 kg — pounds cancel.
Multi-step, 2 pints to liters: 2 pt x (480 mL / 1 pt) x (1 L / 1,000 mL) = 0.96 L — pints cancel, then mL cancel.
If the leftover unit is wrong (e.g., you end with lb²/kg), the factors were flipped. This self-check is why dimensional analysis is the safest method under time pressure.
Temperature conversions
| Direction | Formula |
|---|---|
| Celsius to Fahrenheit | F = (C x 9/5) + 32 |
| Fahrenheit to Celsius | C = (F - 32) x 5/9 |
| Reference | Fahrenheit | Celsius |
|---|---|---|
| Water freezes | 32 F | 0 C |
| Hypothermia threshold | 95 F | 35 C |
| Normal body temp | 98.6 F | 37 C |
| Fever threshold | 100.4 F | 38 C |
| Water boils | 212 F | 100 C |
For F to C, subtract 32 before multiplying by 5/9 — order of operations matters.
Dosage calculations
The core formula:
Desired (D) / Have (H) x Quantity (Q) = amount to give
where D is the ordered dose, H is the strength on the label, and Q is its form (tablet, mL).
- Order 500 mg; have 250 mg tablets: 500/250 x 1 = 2 tablets.
- Order 150 mg; have 100 mg / 5 mL: 150/100 x 5 = 7.5 mL.
Weight-based (pediatric) dosing
- Convert weight: pounds / 2.2 = kilograms.
- Total dose: kg x mg/kg.
- Volume: apply D/H x Q with the available concentration.
A child weighs 55 lb; order is amoxicillin 25 mg/kg/day in 2 divided doses; supply is 250 mg / 5 mL.
- 55 / 2.2 = 25 kg
- 25 x 25 = 625 mg/day
- Per dose: 625 / 2 = 312.5 mg
- Volume: 312.5/250 x 5 = 6.25 mL per dose
Trap: forgetting step 1 and multiplying pounds by mg/kg inflates the dose by 2.2x — a dangerous error the NEX tests deliberately.
Safe-dose-range checks extend this idea: a reference may list 20-40 mg/kg/day. For the 25 kg child that is 500-1,000 mg/day, so a 625 mg/day order is safe to give. If a calculated order falls outside the range, the correct clinical action is to hold and verify — the exam rewards recognizing the unsafe value, not blindly administering it.
A patient weighs 198 pounds. What is their weight in kilograms?
How many milliliters are in 3 tablespoons?
Convert 102.2 F to Celsius.
A provider orders 750 mg of medication. The pharmacy stocks 250 mg/5 mL liquid. How many mL should be given?
There are _____ milligrams in 1 gram.
Type your answer below
A child weighs 44 lb. The medication order is 10 mg/kg. What is the correct dose?
Match each measurement to its metric equivalent.
Match each item on the left with the correct item on the right
Which statements about metric conversions are correct? (Select all that apply)
Select all that apply