Liquid Medication
Giving the Right dose ml by ml

Calculating dosages for liquid medications is also EXTREMELY simple. First, you should master how to calculate pill dosages. After you are comfortable with that, we move on to our next formula.


















I learned this formula in 12th grade chemistry. It works almost ALL of the time for me, as long as I set it up correctly. You answer should always end with the units (mg, ml, units, etc.) that you are looking for. Next, remember that units above and below the line will cancel each other out. Just practice and it will start to make sense.

Here is my secret formula!

  1. Set up your equation. This may take some time to learn, but once you do, it will become simple
  2. Cancel all units that you see on both the bottom AND the top of the equation. Note that if the unit measure is only present once on the top, you can only mark it out once on the bottom, and vice versa.
  3. Now the only math step! Multiply all the numbers on the top, then multiply all the numbers on the bottom. Now divide the top number by the bottom number and WALA you have your answer.

Don’t worry, it is easier than it sounds. Ready? Here is your formula:

Nursing Math Equation for Calculation PO liquids

Let’s Jump Right In

1. The doctor orders 5mg of Robitussin PO daily. Your medication bottle from the pharmacy states 1mg/2ml of Robitussin. There are 30ml in the bottle. How many do you give?

Example 1 For Liquid Medications

Try again!

2. You need to give 40meq of KCL PO x1. You have little cups that state KCL 20meq/5ml. How many mL do you give:

Last example!

3. You need to give 10,000 units of swish and spit Nystatin q6h. You have 5,000units/2ml packages of Nystatin. What to do?

If you are having trouble grasping this concept don’t worry. Most people struggle with it in the beginning. It will just make sense to you one day, at least that is what happened to me. After practicing and practicing, I just had a lightbulb moment one day. Now nursing math is simple to me. Learn this formula before moving on because it is your base and you MUST understand calculating liquid medication before moving on to IV drip calculations.

If you understand calculation for PO liquid medication, move on to IV liquid calculations

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