Basic
drug
calculations
Metric system  Metric basicsThe metric system is
an international standard
of measurement based
on decimals. It is
used to measure weight,
liquids, and
length. The modern
metric system, introduced
in Australia in 1970,
is called the International
System of Units (SI).
Basic units
The metric system
uses a 'basic unit'
for each type of measurement,
represented by a symbol.
Basic units commonly
used in nursing and
midwifery include:
Type of measurement 
Basic unit 
Symbol 
weight (mass) 
gram 



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Variations to the basic unit (smaller or larger amounts)
Below are some of
the common variations
to basic units to show
smaller or larger multiples
of the unit. To
indicate these variations,
a prefix is added to
the basic unit. Note
the symbols
for each prefix. Examples
of everyday objects
using these measurements
are shown.
Common variations: 


Basic units: 

Prefix/symbol: 
micro (µ) 
milli (m) 
kilo (k) 

microgram
(µg or mcg or microgram)
It is impossible to show a microgram!

milligram (mg)
A pinch of salt weighs approximately 1 milligram

gram (g)
A paperclip weighs approximately 1 gram 
kilogram (kg)
1 kilogram of flour 

microlitre (µL)
A syringe can measure microlitres.

millilitre (ml)
The drip from a tap is approximately 1 millilitre.

litre (L)
1 litre of milk



micrometre
Bacteria can be measured in micrometres.

millimetre (mm)
A CD is approximately 1 millimetre deep (120 mm across)

metre (m)
A large adult stride is approximately 1 metre.

kilometre (km)
Roads are measured in kilometres.

If you are new to the metric system it can be helpful to associate real objects with their metric measurements to build up your own awareness of how to estimate using metric measurement. Try these learning activities. (requires Flash player).
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