Metric Conversions

There are many occasions when it is necessary to convert one unit of measurement to another when undertaking drug calculations.

The metric system is based on a number of basic measures or units e.g.

Quantity	Unit	Symbol
Length	metre	m
Mass	gram	g
Volume	litre	l
Time	second	s

Large and small quantities of these units often have a prefix to make writing quantities more compact for example 0.000001g may be written as 1 mcg or 1µg.

Some common units of measurement are:

Prefix	symbol	multiplication factor
mega	M	1,000,000
kilo	k	1000
hecto	h	100
deka	da	10
Unit	1
deci	d	0.1
centi	c	0.01
milli	m	0.001
micro	mc or µ	0.000001

Converting a number from one metric unit to another involves moving the decimal place to the left or the right.

To work out how many decimal places to move:

Write the metric scale

Identify the two units in the problem

Count the number of units from the unit given to the unit desired

Move the decimal point the number of places from the given unit to the desired unit

Example:
Convert 0.5 grams to milligrams.

The decimal place is moved 3 places to the right (as 1 mg = 1000 g).

Mg	-	-	kg	hg	dag	g	dg	cg	mg	-	-	µg
							1	2	3

0.5 g = 500 mg

Example
Convert 375 millilitres to litres (as 1l = 1000ml).

The decimal place is moved 3 places to the left.

Ml	-	-	kl	hl	dal	L	dl	cl	ml	-	-	µl
						3	2	1

375 ml = 0.375 l

Other Calculations
Metric Conversions	Body Mass Index	Tablet Dosages	Fluid Dosages	IV Flow Rates	Dosage by Weight