Key Takeaways
- Measurement/Conversions covers approximately 14 items (~35%) of the NEX math section — the largest subsection
- The metric system uses base units (gram, liter, meter) with prefixes: kilo (x1000), centi (x0.01), milli (x0.001)
- Essential nursing conversions: 1 kg = 2.2 lbs, 1 tsp = 5 mL, 1 tbsp = 15 mL, 1 oz = 30 mL, 1 cup = 240 mL
- Dimensional analysis (factor-label method) is the safest conversion method — units cancel until only the desired unit remains
- Temperature: F = (C x 9/5) + 32 and C = (F - 32) x 5/9; normal body temp is 98.6F / 37C
- Dosage formula: Desired / Have x Quantity = Amount to give
- Weight-based dosing: convert lbs to kg first (divide by 2.2), then multiply by dose per kg
- Always double-check unit conversions — errors in medication dosing can be life-threatening
Measurement & Conversions
Measurement and conversions is the largest subsection of the NEX Mathematics section, comprising approximately 14 items (~35%). These questions are highly nursing-relevant and test your ability to convert between measurement systems accurately.
The Metric System
| Prefix | Abbreviation | Value | 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 between metric units:
- Moving to a smaller unit: multiply (or move decimal right)
- Moving to a larger unit: divide (or move decimal left)
- Each step is a factor of 10
Examples:
- 2.5 L = 2,500 mL (multiply by 1,000)
- 750 mg = 0.75 g (divide by 1,000)
- 3,200 g = 3.2 kg (divide by 1,000)
Essential Nursing Conversions
| Conversion | Value | Category |
|---|---|---|
| 1 kg | 2.2 lbs | Weight |
| 1 inch | 2.54 cm | Length |
| 1 teaspoon (tsp) | 5 mL | Volume |
| 1 tablespoon (tbsp) | 15 mL | Volume |
| 1 fluid ounce (oz) | 30 mL | Volume |
| 1 cup | 240 mL (8 oz) | Volume |
| 1 pint | 480 mL (16 oz) | Volume |
| 1 quart | 960 mL (32 oz) | Volume |
| 1 liter (L) | 1,000 mL | Volume |
| 1 gram (g) | 1,000 mg | Weight |
| 1 mg | 1,000 mcg | Weight |
Dimensional Analysis
Dimensional analysis systematically converts units by multiplying by conversion factors so unwanted units cancel:
Step 1: Write down the starting value with its unit Step 2: Multiply by conversion factors arranged so units cancel Step 3: Solve — only the desired unit should remain
Example 1: Convert 154 lbs to kg
Example 2: Convert 3 tablespoons to mL
Example 3: Multi-step: Convert 2 pints to liters
Temperature Conversions
| Direction | Formula |
|---|---|
| Celsius to Fahrenheit | F = (C x 9/5) + 32 or F = (C x 1.8) + 32 |
| Fahrenheit to Celsius | C = (F - 32) x 5/9 or C = (F - 32) / 1.8 |
Key reference temperatures:
| Description | Fahrenheit | Celsius |
|---|---|---|
| Water freezes | 32°F | 0°C |
| Hypothermia threshold | 95°F | 35°C |
| Normal body temperature | 98.6°F | 37°C |
| Fever threshold | 100.4°F | 38°C |
| Water boils | 212°F | 100°C |
Dosage Calculations
The basic dosage formula:
Desired (D) / Have (H) x Quantity (Q) = Amount to Give
- D = dose ordered by the provider
- H = dose available (on the label)
- Q = the form it comes in (tablets, mL, etc.)
Example: Provider orders 500 mg. Available: 250 mg tablets. D/H x Q = 500/250 x 1 tablet = 2 tablets
Example: Provider orders 150 mg oral suspension. Available: 100 mg/5 mL. D/H x Q = 150/100 x 5 mL = 7.5 mL
Weight-Based Dosing
Many medications, especially in pediatrics, are dosed by patient weight:
- Convert weight to kg: Patient weight (lbs) / 2.2 = weight in kg
- Calculate total dose: Weight (kg) x dose per kg = total dose
- Determine amount to give: Use the dosage formula with available concentration
Example: A child weighs 55 lbs. The order is for amoxicillin 25 mg/kg/day divided into 2 doses. Available: 250 mg/5 mL.
- 55 lbs / 2.2 = 25 kg
- 25 kg x 25 mg/kg = 625 mg/day
- Per dose: 625 / 2 = 312.5 mg
- Volume: 312.5/250 x 5 mL = 6.25 mL per dose
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 has 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 lbs. 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 of the following statements about metric conversions are correct? (Select all that apply)
Select all that apply