The document outlines the metric system, detailing its historical adoption, key units for measurement (gram, liter, meter), and its standardized decimal-based structure used globally for scientific and industrial measurement. It explains the fundamental conversion relationships between different units of length, volume, and weight, and provides guidelines for medication dosages based on body weight. Additionally, it emphasizes common metric prefixes, basic rules for measurement, and conversion techniques between different metric units.

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UNIT 4
The Metric System

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Key Terms
• Gram
• Liter
• Meter

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Metric System
• First proposed in 1670 by Gabriel Mouton
• Adopted in 1801 by French National
Assembly
• Official standard for scientific and industrial
measurement in 92% of world
• Measured in units of 10
• Utilizes concept of decimal point
(continues)

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Metric System
• Provides simple, flexible, accurate way to
measure length, volume, and weight
• Medication dosages may be
– In micrograms
– In milligrams
– In grams
– Per kilogram of body weight
(continues)

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Metric System
• Volume of medication may be in
– Milliliters
– Cubic centimeters
• Other measurements
– BP measured in millimeters of mercury (mm Hg)
– Wound and lesion size measured in centimeters
– Organs measured in grams
(continues)

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Metric System
• Laboratory results measured in:
– Micrograms
– Milligrams
– Grams per deciliter
– Units per liter

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Basic Rules
• Whole numbers designated by Arabic
numbers
• Decimal fractions used for numbers less
than 1
• Prefixes written in lowercase
• Abbreviations are same for singular or
plural

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Metric System
• Uses 14 prefixes
• Each prefix based on multiple of 10
• Medical field uses seven most common
prefixes

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Metric Prefixes
Micro- One millionth
Milli- One thousandth
Centi- One hundredth
Deci- One tenth
Deka- Ten
Hecto- One hundred
Kilo- One thousand

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Fundamental Units
Meter Length
Liter Volume
Gram Mass/Weight

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Length
• Meter is fundamental unit of length
– 1 meter = 39.37 inches or 3.28 feet
– 1 inch = approximately 2.5 centimeters

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Length
Meter (m) Length
1 millimeter (mm) 0.001 meter
1 centimeter (cm) 0.01 meter
1 decimeter (dm) 0.1 meter
1 meter (m) 1 meter
1 dekameter (dam) 10 meters
1 hectometer (hm) 100 meters
1 kilometer (km) 1,000 meters

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Volume
• Liter is fundamental unit of volume
– 1 liter = 1.056 quarts
– 1 liter = 0.26 gallon
– 1 liter = 2.1 pints
– 1 mL = 1 cc
(continues)

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Volume
• Liter is fundamental unit of volume (cont’d)
– Amount of space occupied by 1 milliliter is equivalent to
1 cubic centimeter
– 1 mL water = 1 g in weight
– 15 mL = 1 tablespoon

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Volume
Liter (L) Volume
1 milliliter (mL) 0.001 liter
1 centiliter (cL) 0.01 liter
1 deciliter (dL) 0.1 liter
1 liter (L) 1 liter
1 dekaliter (daL) 10 liters
1 hectoliter (hL) 100 liters
1 kiloliter (kL) 1,000 liters

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Weight
• Gram is fundamental unit of solids, mass, or
weight
– 1 cc or 1 mL of water = 1 g
– 1 g = approximately 15 grains
– 1 g = 0.035 oz

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Weight
Gram (g) Weight
1 milligram (mg) 0.001 gram
1 centigram (cg) 0.01 gram
1 decigram (dg) 0.1 gram
1 gram (g) 1 gram
1 dekagram (dag) 10 grams
1 hectogram (hg) 100 grams
1 kilogram (kg) 1,000 grams

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Common Equivalents
• 2 ½ cm = 1 inch
• 1,000 mL or cc = 1 liter
• 1,000 mcg = 1 mg
• 1,000 mg = 1 g
• 1,000 g = 1 kg
• 1 kg = 2.2 lb

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Conversions
• Set up proportion using metric equivalents
• Assign x as value of unknown factor
• Solve proportion as learned in Unit 3

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Moving the Decimal
• If converting from larger to smaller,
multiply by decimal value of smaller unit
(move decimal right)
• If converting from smaller to larger, divide
by decimal value of smaller unit (move
decimal left)

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Dosage Based on Body Weight
• Some medications are ordered as mg/kg
• Weight of patient must be expressed in kg

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Calculating Dose
• Convert weight to kg
• Calculate dosage based on weight
• Determine number of doses per day
• Calculate amount of medication per dose