COURSE READINESS ASSESSMENT
FOR
PHYSIOLOGY
THE METRIC SYSTEM
The International System (SI system) of units
or metric system
 A system of measurements and units commonly used in science
 In comparison to the English system, it is easy to describe units
smaller or larger than the basic unit by using prefixes
 Converting from one metric prefix to another is relatively simple
because the prefixes differ by powers of ten
Common metric measurements and units
Meter
(m)
Gram
(g)
Liter
(l or L)
Degree Celsius
(oC)
Second
(s)
MEASUREMENT Length
Mass
Volume
Temperature
Time
BASE UNITS
Larger
Commonly used metric prefixes
Prefix symbol
Prefix name
Prefix value
Fraction or Multiple
Power
k
kilo
one thousand
1,000
103
M
mega
one million
1,000,000
106
G
giga
one billion
1,000,000,000
109
1
10
Smaller
BASIC UNIT: m,g,l
d
deci
1/10
0.1
10-1
c
centi
1/100
0.01
10-2
m
milli
1/1,000
0.001
10-3
µ
micro
1/1,000,000
0.000 001
10-6
n
nano
1/1,000,000,000
0.000 000 001
10-9
Length: Meters
 The basic unit of distance in the metric system is the meter (m),
which is slightly more than a yard (approximately 39.37 inches).
 Distances larger than a meter are measured in units that are:
Abbreviation
Unit
Prefix value
Multiple of a Meter
Power
km
kilometer
one thousand
1,000
103
Mm
megameter
one million
1,000,000
106
Gm
gigameter
one billion
1,000,000,000
109
Examples:
• a kilometer (km) is 1,000 meters, or 103 meters
• a megameter (Mm) is 1,000,000 meters, or 106 meters
Length: Meters
 Distances smaller than a meter are subdivided into smaller units:
Abbreviation
Unit
Prefix value
Fraction of a Meter
Power
dm
decimeter
1/10
0.1
10-1
cm
centimeter
1/100
0.01
10-2
mm
millimeter
1/1,000
0.001
10-3
µm
micrometer
1/1,000,000
0.000 001
10-6
nm
nanometer
1/1,000,000,000
0.000 000 001
10-9
Examples:
• a decimeter (dm) is a tenth of a meter, or 10-1 meter
• a millimeter (mm) is a thousandth of a meter, or 10-3 meter
Mass: Grams
 The basic unit of mass (weight) in the metric system is the gram (g).
 A gram is the approximate mass (or weight) of a paper clip.
 When measuring masses (weights) that are larger or smaller than a gram,
larger or smaller units are likewise created:
Abbreviation
Unit
Prefix value
kg
kilogram
1,000
Mg
Megagram
1,000,000
cg
centigram
1/100
mg
milligram
1/1,000
Examples:
• a kilogram measures 1,000 grams
• a Megagram (Mg) measures 1,000,000 grams
• a decigram (dg) measures tenths of a gram
• a centigram (cm) measures hundredths of a gram
• a milligram (mg) measures thousandths of a gram
• a microgram (µg) measures millionths of a gram
Volume: Liters
 The basic unit of volume is a liter (l or L), which is slightly more than a
quart.
 To measure volumes that are more or less than a liter, larger or smaller units
are created in exactly the same way as for the meter:
Abbreviation
Unit
Prefix value
kl
kiloliter
1,000
ML
Megaliter
1,000,000
cl
centiliter
1/100
mL
milliliter
1/1,000
Examples:
• a kiloliter measures 1,000 liters
• a Megaliter (ML) measures 1,000,000 liters
• a deciliter (dl) measures tenths of a liter
• a centiliter (cl) measures hundredths of a liter
• a milliliter (ml) measures thousandths of a liter
• a microliter (µl) measures millionths of a liter
Temperature: Degrees Celsius
 Definitions
Also called the centigrade scale
 0° Celsius = 32° Fahrenheit = water freezes
 100° Celsius = 212° Fahrenheit = water boils
 Therefore, 1°C = 1.8°F
 Conversions
 ° Celsius = 5/9 x (° Fahrenheit - 32°)
 ° Fahrenheit = (9/5 x ° Celsius) + 32°
Celsius
-10°
0°
10°
20°
30°
40°
Body Temperature
Frigid
Cold - Water Freezes
Cool
Comfortably Warm
Hot
Very Hot
Fahrenheit
14°
32°
50°
68°
86°
104°
Time: Seconds
 Metric or decimalized time is based on the solar day
(i.e., one revolution of the Earth).
 This day is then divided into units of tenths, hundredths,
thousands, etc. that are used to keep and tell time.
 The base unit is a second (s). There are 100 metric seconds
in a metric minute.
Converting within the metric system
 Converting from one metric prefix to another is a simple matter of
multiplying or dividing by the power of 10 difference between them
 Basically, you are determining the direction to move the decimal and the
number of places to move it
 One way to determine this is to draw a horizontal "metric line" like the one
shown below. Each vertical line represents a decimal place. Common metric
prefixes are written below the line.
Note: unless Mega (M) and micro (μ) are needed, the basic unit and three
prefixes to the left and right of the basic unit will be enough.
|-------|-------|-------|--------|---------|---------|---------|---------|---------|-------|-------|-------|
M
k
h
da basic unit d
c
m
μ
m, l, g
 To convert from one prefix to another: Locate the starting prefix, then move the
decimal in the direction and number of places needed to reach the desired
prefix.
Converting within the metric system
 A microgram is smaller than a milligram by a factor of 1,000, so a
given number of milligrams should be equal to many more
micrograms, or 1000 times as many.
 ie.) 3 milligrams = 3000 micrograms
or
3 mg = 3000 µg
 A liter is larger than a milliliter by a factor of 1,000, so a given
number of milliliters should be equal to fewer liters, or 1/1,000 as
many.
 ie.) 3 milliliters = 0.003 liters
|-------|-------|-------|--------|---------|---------|---------|---------|---------|-------|-------|-------|
M
k
h
da basic unit d
c
m
μ
m, l, g
Summary: The metric (SI) system
 The SI or metric system is system of units commonly used in science
 There are basic metric units for measurements such as length, mass, volume,
temperature, and time
 Metric prefixes describe powers of ten larger or smaller than the basic metric
unit
 Some common prefixes, their symbols, and their relationships:
Prefix
Mega
Kilo
Basic Unit
Deci
Centi
Milli
Micro
Nano
Symbol or abbreviation
M
k
m, l, g
d
c
m
mc or μ
n
Value
1,000,000
1,000
1
1/10
1/100
1/1,000
1/1,000,000
1/1,000,000,000