This how to guide on drug dosage calculations has been created for student nurses pharmacy students pre registration pharmacists and pharmacy technicians the aim of this guide is to learn how to calculate a drug dosage from the stock strength this learning is divided into three parts part 1 will define the two formulas that can be used to calculate the drug dose required from stock . 74 thoughts on dosage calculations the easy way dr rachel silva dnp may 9 2015 at 1106 am what an excellent resource you have created for nursing students i certainly wish i could have had this to discover back when i was in nursing school but we barely knew what computers were haha. Often some type of calculation prior to medication administration is needed drug calculations can be simple or more complex regardless of the drug to be administered careful and accurate calculations are necessary to help prevent medication errors practicing drug calculations will develop stronger and more confident math skills. Some drug calculations may involve working out the volume of solution needed to give the required dose of a drug one way to tackle these types of questions is to set up a simple equation where x is the variable you are trying to find for example. The rule for maximum dosage volume to be administered per intramuscular injection an average 150 lb adult 3 ml maximum for deltoid site is 2 ml children age 6 to 12 years 2 ml birth to 5 years 1 ml