As a nurse, you are often asked to calculate and administer dosage amounts quickly, especially in pain management. Accuracy is imperative; a miscalculation can lead to overdose, such as for intravenous opiates or local anaesthetics. Miscalculations are especially probable when dealing with more complex computations, such as in paediatric nursing, where doses are calculated based on the additional factor of body weight. Whether nurses should use calculators or not, however, is contested. Some argue that calculators, especially for complex calculations, should be allowed for the benefit of speed and accuracy. The UK Nursing and Midwifery Council recommends that nurses should not depend on calculators excessively and should ensure they have developed basic mathematics competency. Usually, nursing programmes require an understanding of maths up to algebra (GCSE Maths of C or higher). Some may require statistics and probability as well.
On occasion you want to verify your calculations, feel free to use our handy basic dosage calculator below, which utilises the mnemonic, what you want x what's it's in / what you've got. Another way to describe the formula is: (desired amount/amount on hand) x volume.
An example of when to use the calculator would be: If you have an ampoule of 500mg in 4ml, and you need 200mg, what volume of the ampoule do you need? Answer: 1.6ml (source: nursingtimes.net).
A few other helpful formulas are:
Infusion Rate: Dose (mg/hr) x volume in syringe (ml) / Amount in syringe (mg)
IV Drips in mcg/minute: (mg/ml) x (1000mcg/1ml) x (ml/1 hour) x (1hour/60 minutes) = mcg/minute
*divide by kg to get mcg/kg/minute
IV Drips in units/hour: (desired amount/amount on hand) x volume = units/hour (# ml x units/ml = dose)
Young's Formula (paediatrics, dose for 1-12 year olds): (age in years)/(age + 12) x (adult dose)
Dilling's Formula (paediatrics, dose for 4-20 year olds): (age in years)/20 x (adult dose)
Fried's Formula (paediatrics, age adjustment for infants): (age in months)/150 x (adult dose)