Dosage Calculations the Easy Way!

When it comes to doing nursing math, which is essentially figuring out dosage amounts, the absolute best, easiest and most foolproof way to do it is by using dimensional analysis. You may remember it from your chemistry class and loved it even then ;-). In this post I will show you how to use dimensional analysis to solve any dosage calculation, even the tricky weight-based ones.

Level 1 Dimensional Analysis
We’ll start at level 1….super easy ones to give you a feel for the technique. Ready? Your order reads:
In dimensional analysis, you always start with what’s ordered. In this case it’s 650 mg of acetaminophen. You will write this as a fraction, with 650 on top and 1 on the bottom like so: 

Next, you need to know what dosage amounts your medication comes in. This is known as the conversion factor. In the case of good ol’ Tylenol, we check our blister pack and see that it’s 325 mg per tablet. The next step is to add the conversion factor also as a fraction. Since mg is at the top of our first fraction, it will go on the bottom of our next one so that they cancel each other out. Like so:
As we move forward into more complicated calculations, it will become more evident that you know when to stop conversions when you are left only with the information needed to give the dose. In this case, we want to know how many tablets to give the patient. Everything except for tablets is crossed out, so we know we are ready to do some math.

1) Multiply across the top: 650 x 1
2) Then divide across the bottom: ÷ 325.
What answer did you get?

Let’s do one more easy one…
For this calculation, let’s assume midazolam comes in 5 mg tablets. I have no idea if it does, but we’re just practicing so it’s all good. Hopefully, you’ve set up your calculation like this:
Next, cross out the units that are the same…in this case it’s mg.

We are now left with X # of tablets to give our 1 patient. Voila! Now,  do your calculation!

OK…you have the hang of that now? That’s a simple calculation with one conversion. What if you have multiple conversions, medications dosed by weight or even medications dosed by weight AND time? My course Confident Calculations teaches you how to perform all types of medication math with 100% accuracy. Every. Single. Time.

We start at the very beginning with the basics and then build your skills and confidence until you are able to easily master even the most challenging calculations. I also teach you a method that gets you thinking critically about dosage calculations questions…they’re not just math problems. They are concept problems that often require critical thinking (not just multiplying and dividing!).

How do you know if Confident Calculations can help? Give this calculation a try:

Tania is receiving a loading dose of phenytoin IV for status epilepticus. To avoid cardiac complications, this powerful medication must be administered slowly at a rate not to exceed 50mg per minute. The medication comes pre-mixed from the pharmacy at a concentration of 5mg/ml. If Tania is to receive a total dose of 700 mg, what is the minimum amount of time you should take to infuse this medication?

How’d you do? If you got stuck, had trouble figuring out where to start, weren’t sure what the question was asking or couldn’t get your conversions to cancel out…then you will LOVE the confidence and skills you’ll get from Confident Calculations. I hope to see you there!

Want to learn pharmacology in 5 minutes or less? Sign up to get notified when my audio-based program Fast Pharmacology launches in Fall 2023!

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