ABSTRACT
It is essential to use the same units throughout a medicine calculation – you cannot
work with both micrograms and milligrams, or millilitres and litres. Therefore you
need to convert the medicine doses in the calculation into the same units. It does not
matter which unit you change them into. However, most people find whole numbers
easier to work with, even if they are very large (Lumsden and Doodson 2003). There
is a simple rule for conversion which is the rule of thousands: everything that needs
converting is achieved by either dividing or multiplying by a thousand. This is because:
With a few exceptions, these are the units used in medicine prescriptions. So, to
convert 5 milligrams (mg) into micrograms (mcg), you need to multiply by 1000
(equals 5000 micrograms).
