Metric System in Pharmacy Calculation


There are three systems of measurement used in pharmacy calculations, which are – metric system, apothecary system and avoirdupois system. Where the metric system is the internationally recognized decimal system of weights and measures. Which is also called the International System of Units (SI).

Metric System

The metric system is a most commonly used a decimal system with all multiples and divisions based on a factor of 10. It is also the legal standard of measurement for pharmacy and medicine in the United States. It allows for quick and easy conversions between different systems of measurement. The basic units of measurement in the metric system are the meter (m), liter (L), and gram (g).

Metric weight

  • 1 Kg =1,000 g = 1,000,000 mg = 1,000,000,000 micrograms = 1,000,000,000,000 nanograms
  • 1 g = 1,000 mg = 1,000,000 micrograms = 1,000,000,000 nanograms
  • 1 mg = 1,000 micrograms = 1,000,000 nanograms
  • 1 micrograms = 1,000 nanograms

Metric volume

  • 1 L =1,000 mL = 1,000,000 microliter
  • 1 mL = 1,000 microliter

Metric length

  • 1 kilometre = 100 decametre = 1000 metres
  • 1 metre = 10 decimetre = 100 centimetre = 1000 millimetre

Few commonly used conversions between household and metric

  • 1 teaspoon = 5 milliliters
  • 1 tablespoon = 15 milliliters
  • 1 cup (eight ounces) = 240 milliliters
  • 1 pint (sixteen ounces) = 480 milliliters

Pharmacy students need to be familiar with various systems of measurement to perform pharmaceutical calculation. Being able to understand the metric system and also convert between the units of measurement is absolutely critical when study a pharmacy degree.

Correct Use of Metric System

1. Unit names and symbols generally are not capitalized except when used at the beginning of a sentence or in headings. However, the symbol for liter (L) may be capitalized or not.


  • Correct: 4L or 4l, 4mm, and 4g 
  • Incorrect: 4Mm and 4G.

2. Periods are not used following metric symbols except at the end of a sentence.


  • Correct: 4 mL and 4g, 
  • Incorrect: 4 mL. and 4 g.

3. Symbols should not be combined with spelled-out terms in the same expression.


  • Correct: 3mg/mL, 
  • Incorrect: 3mg/milliliter.

Pharmacy Calculation Using Metric System


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