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Textbook
1. Medical assistant
2. Electronic records
3. Medical terminology and anatomy
4. The fundamentals of infection control
5. Introduction to vital signs
6. The patient interview and history
7. The physical examination
8. Appointment scheduling
9. Insurance billing
10. Diagnostic coding and the ICD-10-CM System
11. Procedural coding
12. Medical billing and reimbursement essentials
13. Assisting with medical specialties
14. Assisting with the musculoskeletal system
15. Assisting with the cardiovascular system
16. Assisting with the respiratory system
17. Assisting with the nervous system
18. Anatomy and physiology of the urinary system
19. Assisting in obstetrics and gynecology
20. Assisting in endocrinology
21. Assisting in ophthalmology & otolaryngology
22. Assisting in gastroenterology
23. Assisting in the immune & lymphatic systems
24. Assisting in pediatrics: the developmental stages and care
25. The medical assistant’s role in caring for the older patient
26. The role of the medical assistant in physical therapy examination and assessment
27. Preparing for minor surgery: room, solutions, and supplies
28. Introduction to the clinical laboratory
29. Urinalysis
30. Blood collection
31. Analysis of blood
32. Electrocardiography and heart structure
33. The principles of pharmacology
34. Essential calculations and measurement systems
34.1 Math basics for medications
34.2 Drug labels and core mathematical principles
35. Solid, liquid, & solutions medication doses
36. Administering medications
37. Metabolism and core nutrient roles
38. Medical emergencies in the healthcare setting
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34.1 Math basics for medications
Achievable CCMA
34. Essential calculations and measurement systems
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Math basics for medications

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Medical math and dosage calculations

All medical assistants should be able to convert between units of measure. It is also important to be able to accurately calculate medication dosages. This section discusses different types of math problems that a medical assistant should be able to solve. Please note that in some states, calculating medical dosages may be outside the legal scope of practice for medical assistants. State laws vary.

The following sections present guidelines for writing and calculating dosages. The medical assistant should always verify answers for dose calculations with a co-worker or the provider.

Healthcare rules when writing numbers

With medications, it is important to be accurate in calculating and documenting amounts. There are four rules to follow when writing medication dosages in healthcare:

Rule 1: Use the correct unit abbreviation

Follow the number with the correct abbreviation for the unit of measure. Leave a space between the number and the abbreviation. Do not use a period with the abbreviations.

Correct examples

  • 2 mg
  • 10 mL

Incorrect examples

  • mg.2
  • 10mL

Rule 2: Write fractions as decimals

Write a fraction of a dose as a decimal.

Correct examples

  • 0.2 mg
  • 0.5 mg

Rule 3: Use a leading zero

If the dose is less than 1, place a zero to the left of the decimal point. This reduces the risk of misreading the dose as a whole number.

Correct examples

  • 0.75 mcg
  • 0.2 mL

Incorrect examples

  • .75 mcg
  • .2 mL

Rule 4: Do not use trailing zeros

Do not place a decimal point and a zero after a whole number. This can be easily misread, and the patient would be given an overdose of medication.

Correct examples

  • 2 mL
  • 5 mL

Incorrect examples

  • 2.0 mL
  • 5.0 mL

Rounding numbers

When you calculate answers, sometimes the number needs to be rounded.

Steps for rounding

  1. Find the place value where you want to end up.
  2. Look at the number to the right of the place value.
    • 4 or below → drop the remaining digits.
    • 5 or above → add 1 to the rounded digit and drop the remaining digits.

Examples

Example 1

569.365

The 3 is in the tenths place. The next digit is 6, so round up.

Answer: 569.4

Example 2

339.926

The 9 is in the tenths place. The next digit is 2, so drop the remaining digits.

Answer: 339.9

Healthcare rules when writing numbers

  • Use correct unit abbreviations with space, no period (e.g., 2 mg, 10 mL)
  • Write fractions as decimals; use leading zero if <1 (e.g., 0.5 mg, 0.2 mL)
  • Do not add trailing zero after whole numbers (e.g., 2 mL, not 2.0 mL)

Rounding numbers

  • Round to nearest tenth (one decimal place)
  • If next digit is 5 or more, round up; if 4 or less, round down

Roman numerals

  • Know basic Roman numerals (i, v, x, l, c, d, m)
  • Used occasionally in medication orders, often in lowercase

Measurement systems

  • Three systems: apothecary, household, metric
  • Metric system is most accurate and preferred in healthcare

Apothecary system

  • Oldest system; uses grains (gr) for weight, minims for volume
  • Abbreviations before Roman numerals (e.g., gr v)
  • Largely replaced by metric system

Household system

  • Common abbreviations: gtt (drop), tsp (teaspoon), tbsp (tablespoon), fl oz (fluid ounce), oz (ounce), qt (quart), pt (pint), lb (pound)
  • Used for patient instructions, less precise than metric

Converting between household and metric equivalents

  • Use proportion method: set up equivalent fractions, cross-multiply, then divide
  • Keep units and labels consistent on both sides of equation

Metric system

  • Weight: grams (g); Volume: liters (L); Length: meters (m)
  • Convert within the same base unit (e.g., g to mg, cm to mm)
  • Use proportion method for conversions (e.g., 1 g = 1000 mg)

Temperature conversion

  • Fahrenheit to Celsius: (°F − 32) ÷ 1.8 = °C
  • Celsius to Fahrenheit: (°C × 1.8) + 32 = °F
  • Round answers to nearest tenth

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Math basics for medications

Medical math and dosage calculations

All medical assistants should be able to convert between units of measure. It is also important to be able to accurately calculate medication dosages. This section discusses different types of math problems that a medical assistant should be able to solve. Please note that in some states, calculating medical dosages may be outside the legal scope of practice for medical assistants. State laws vary.

The following sections present guidelines for writing and calculating dosages. The medical assistant should always verify answers for dose calculations with a co-worker or the provider.

Healthcare rules when writing numbers

With medications, it is important to be accurate in calculating and documenting amounts. There are four rules to follow when writing medication dosages in healthcare:

Rule 1: Use the correct unit abbreviation

Follow the number with the correct abbreviation for the unit of measure. Leave a space between the number and the abbreviation. Do not use a period with the abbreviations.

Correct examples

  • 2 mg
  • 10 mL

Incorrect examples

  • mg.2
  • 10mL

Rule 2: Write fractions as decimals

Write a fraction of a dose as a decimal.

Correct examples

  • 0.2 mg
  • 0.5 mg

Rule 3: Use a leading zero

If the dose is less than 1, place a zero to the left of the decimal point. This reduces the risk of misreading the dose as a whole number.

Correct examples

  • 0.75 mcg
  • 0.2 mL

Incorrect examples

  • .75 mcg
  • .2 mL

Rule 4: Do not use trailing zeros

Do not place a decimal point and a zero after a whole number. This can be easily misread, and the patient would be given an overdose of medication.

Correct examples

  • 2 mL
  • 5 mL

Incorrect examples

  • 2.0 mL
  • 5.0 mL

Rounding numbers

When you calculate answers, sometimes the number needs to be rounded.

Steps for rounding

  1. Find the place value where you want to end up.
  2. Look at the number to the right of the place value.
    • 4 or below → drop the remaining digits.
    • 5 or above → add 1 to the rounded digit and drop the remaining digits.

Examples

Example 1

569.365

The 3 is in the tenths place. The next digit is 6, so round up.

Answer: 569.4

Example 2

339.926

The 9 is in the tenths place. The next digit is 2, so drop the remaining digits.

Answer: 339.9

Key points

Healthcare rules when writing numbers

  • Use correct unit abbreviations with space, no period (e.g., 2 mg, 10 mL)
  • Write fractions as decimals; use leading zero if <1 (e.g., 0.5 mg, 0.2 mL)
  • Do not add trailing zero after whole numbers (e.g., 2 mL, not 2.0 mL)

Rounding numbers

  • Round to nearest tenth (one decimal place)
  • If next digit is 5 or more, round up; if 4 or less, round down

Roman numerals

  • Know basic Roman numerals (i, v, x, l, c, d, m)
  • Used occasionally in medication orders, often in lowercase

Measurement systems

  • Three systems: apothecary, household, metric
  • Metric system is most accurate and preferred in healthcare

Apothecary system

  • Oldest system; uses grains (gr) for weight, minims for volume
  • Abbreviations before Roman numerals (e.g., gr v)
  • Largely replaced by metric system

Household system

  • Common abbreviations: gtt (drop), tsp (teaspoon), tbsp (tablespoon), fl oz (fluid ounce), oz (ounce), qt (quart), pt (pint), lb (pound)
  • Used for patient instructions, less precise than metric

Converting between household and metric equivalents

  • Use proportion method: set up equivalent fractions, cross-multiply, then divide
  • Keep units and labels consistent on both sides of equation

Metric system

  • Weight: grams (g); Volume: liters (L); Length: meters (m)
  • Convert within the same base unit (e.g., g to mg, cm to mm)
  • Use proportion method for conversions (e.g., 1 g = 1000 mg)

Temperature conversion

  • Fahrenheit to Celsius: (°F − 32) ÷ 1.8 = °C
  • Celsius to Fahrenheit: (°C × 1.8) + 32 = °F
  • Round answers to nearest tenth

More from Essential calculations and measurement systems

  • Drug labels and core mathematical principles