Dosage Calculations: IV Drip Factor Formula

SimpleNursing Editorial Team Dec 3, 2018
Female woman nurse holding IV bag and observing drip factor for a woman patient in a hospital bed

Giving patients the proper medication and dose is fundamental to their welfare and overall health. That’s why it’s crucial to remember the drip factor formula when administering patient IVs. 

Administering IVs is one of the primary responsibilities of the healthcare team, especially the nurses. 

And when it comes to nursing care, nursing students need to understand that the dose introduced to their clients may precipitate unwanted errors that may lead to severe complications.

We’re going over the essential relevance of accurate dosage calculation, primarily focusing on intravenous drip factor, or the drip rates. 

How to Calculate Drip Rate

When you’re starting an IV, it’s important to make sure that your drip rate is right – not too much or too little. This will ensure that the patient receives the correct amount of medication.

The drip factor is needed to calculate the drops per minute/flow rate. Flow rate is measured by counting the number of drops (shown as “gtt”) that fall into the drip chamber each minute. 

As opposed to drip factor, the drop factor is the number of drops in 1 mL of solution. Drop factors are printed on IV tubing packages.

a nurse's gloved hands holding IV drop line

Calculating intravenous drip rates (gtt/min) would include these main elements:

  • Total volume – The amount of the desired liquid infusion in mL.
  • Drip factor – The number of drops (gtts) in one milliliter (mL) of solution delivered by gravity.
  • Time – The planned time of the infusion, divided by minutes or hours.

What is Gtt?

In nursing, gtt is used to measure medications that are given intravenously or subcutaneously. It allows nurses to easily see if patients are getting the right amount of medication, without needing a scale at every bedside.

Gtt to mL Conversion Chart

If you forgot how to convert gtt to mL, here’s a table to help:


Choosing the right tubing is also important in ensuring patients get the right amount of medication they need.

Macrotubing vs Microtubing

There are two main types of IVs When dripping patients’ fluids: macrodrip tubing and microdrip tubing (also referred to as macrotubing and microtubing). 

Macrodrip tubing is wider, produces larger drops, and is available in three sizes: 10, 15, or 20 drops per mL (gtt/mL). 

Macrotubing allows nurses to use larger tubing on drip sets and administer more fluid. This technique is useful when dealing with patients needing more medication at a faster rate.

Something to consider when using macrodrip tubing is in some cases the drip factor may be too low. Depending on the patient, they might not receive enough fluid and could suffer dehydration. 

Microdrip tubing is narrower, producing smaller drops with typically a drip factor of 60 gtts/mL. This is especially useful in pediatrics and when administering fluids with a narrow tolerance range.

The drip factor of microtubing is typically high (about 0.5) – and administering too much fluid to a patient can cause them to become bloated and uncomfortable.

Calculating these types of formulas is going to help your courses, exams, and nursing career.

Need a refresher on how to start an IV?

The Drip Factor Formula

With all these components and elements, let’s plug them into the formula needed to figure out flow rate. The formula for calculating the IV flow rate (drip rate) is:

  1. Total volume (in mL) 
  2. Divided by time (in min)
  3. Multiplied by the drop factor (in gtts/mL)
  4. Which equals the IV flow rate in gtts/min.

So, the drip factor formula to find flow rate usually goes as:

Total volume x drip factor ÷ time = flow rate (gtt/min)

Applying the Drip Factor Formula

A usual scenario inside a healthcare institution will be a physician ordering normal saline to be infused for a specified period. So you must determine how many drops (gtt) of normal saline you should give the patient in a minute.

What this would look like:

  1. Calculating the intravenous flow rate for 1 liter of normal saline in 8 hours. The drop factor is commonly around 15 gtt/mL. 
  2. Taking note that 1 liter of normal saline equals 1,000 mL, and time should always be 60 minutes. Depending on the physician’s order, time should be multiplied by 60 minutes. In this case, 60 minutes will be multiplied by 8.

So let’s plug in the numbers. Let’s say a doctor has ordered 12000 mL of saline to infuse over 6 hours. You have macrodrip tubing with a drop factor of 10 gtts/mL. Calculate how many gtts/min to set as the IV flow rate.

The formula would look like this:

1,200 mL x 10 gtts/mL ÷ 360 min = 33.33 or 33 gtts/min

To lay it out, 1,200 mL divided by 360 minutes (6 hours), then multiplied by 10 gtts/min equals to 33.33, rounded to 33 gtts/min.

Test this formula out with differing factors until it sticks. You won’t regret it on your next exam or clinical!

Drip Factor Mnemonic

To put together the drip rate formula faster, you can use a mnemonic device that’ll stick with you. Just remember, “TV will make you deaf over time,” which is:

  • TVtotal volume
  • Deaf = DF or drip factor
  • Over = divided by (or over)
  • Time = time prescribed by the physician

Before calculating IV administration, don’t forget to write down the statement, “TV will make you deaf over time,” or repeatedly say it inside your head so that you are equipped with the correct formula.

Find more useful nursing mnemonic devices here

Unlock More Nursing School Resources 

Nurses do a lot of math. Whether it’s calculating a patient’s BMI, figuring out how much fluid they need to drink, or coming up with a formula for IV drip factors, nurses spend their days crunching numbers in their head.

In nursing school, remembering this formula can help you ace any IV-related test. And after graduation, it’ll help you determine the right amount of fluid that needs to be administered to patients.

IV formulas are just one piece of the studying puzzle – you’ll need more to pass your nursing school classes. Taking practice quizzes, overviewing NCLEX questions, and using study guides can get you far as a nursing student.

Sign up today and boost your studying game.

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