The keys to success in this field are: Knowing what is happening in the calculation rather than blindly following a formula. Setting up your calculations mathematically correct. 5 g (1000 mg/g) = 5000 mg is correct. 5 g x 1000 = 5000 mg is incorrect. Unit conversions, dosage calculations, percent problems, and IV flow rate problems can all be solved using a simple and safe method called dimensional analysis (DA). If you take a couple of evenings to learn this method, you will save yourself hours of trying to learn a long list of formulas. These problems all have the same three parts: The Units of the Answer: Think of it as the destination. A Given: This is what is given to start the problem and what is changed into the answer. One or More Ratios: These are the tools used to change the units of the given into the units of the answer. Examples: Unit Conversion: How many mL in 3.5 L. 3.5 L is the given. mL is the unit of the answer. The ratio is 1000 mL/L 3.5 L (1000 mL/L) = 3500 mL L cancel out and you are left with mL in the answer. Dosage Calculation: A patient is ordered 500 mg of a drug which is available in an oral suspension of 250 mg/5 mL. How many mL will you administer? 500 mg is the given. mL is the unit of the answer. The ratio is 250 mg/5 mL 500 mg (5 mL/250 mg) = 10 mL In this case, we had to flip the ratio upside down, which is permissible. Percent Problem: Convert 0.458 to a percent. 0.458 is the given, % is the unit of the answer and 100% is the ratio. 0.458 (100%) = 45.8% IV Flow Rate: An IV is running at 30 mL/h with a drop factor of 20 (20 drops/mL), how many drops/min is that? 30 mL/h is the given. Drops/min are the units of the answer. 20 drops/mL and 60 min/h are the ratios. 30 mL/h (1 h/60 min) (20 drops/mL) = 10 drops/min Unfortunately, there is not enough space here to go into all the details of this method, but you can PM me and I will send you some study material. Also, I am always glad to help with specific calculation questions. Brad Wojcik, PharmD Dosage Calculations PDF-B.Wojcik.pdf