How to do 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 1g.

Some common units of measurement are:

Prefix symbol multiplication factor

Prefix

Symbol

Multiplication Factor

mega

M

1,000,000

kilo

k

1,000

hecto

h

100

deka

da

10

Unit

e.g. g, m, l or s

1

deci

d

0.1

centi

c

0.01

milli

m

0.001

micro

mcg or

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:

  1. Write the metric scale
  2. Identify the two units in the problem
  3. Count the number of units from the unit given to the unit desired
  4. Move the decimal point the number of places from the given unit to the desired unit

Example 1:

Convert 0.1 grams to milligrams.

The decimal place is moved 3 places to the right.

Mg  - - kg hg dag g dg cg mg - - g 

0.1 g = 100 mg

Example 2:

Convert 375 millilitres to litres.

The decimal place is moved 3 places to the left.

Ml  - - kl hl dal l dl cl ml - - l 

375 ml = 0.375 l