Calculating IV Drip Rates: IV Pump Rate Formula Made Easy

by Sara Alvarado

Updated May 10, 2024
Math and nursing are an inseparable duo. That’s because nurses always have to make calculations using doctor prescriptions to know how much of a drug they should give to a patient.

When it comes to IV infusions, the doctor’s prescription says how much of the fluid should be given and over how many hours. The nurse uses that information in the IV pump rate formula to calculate the correct IV drip rate.

So, what exactly is IV drip rate, and why do nurses have to calculate it? How is the IV drip rate calculated, and how does the nurse use the calculations to set the infusion pump rate?

Those are too many questions together, but I’ll answer them for you one by one in this article. Better still, I’ll simplify the IV pump rate formula by showing you how to calculate IV drip rate step by step. So, let’s start with defining IV drip rate.
Calculating IV Drip Rate

1. What is IV Drip Rate

Infusion fluids are delivered in drops from the fluid reservoir through the IV tubing to the patient’s body. The rate at which these drops move from the reservoir into the patient’s body is what we describe as the IV drip rate.

More precisely, the IV drip rate refers to the number of fluid drops delivered through the infusion set to the patient’s circulatory system in one minute.

The IV drip rate is different from the dosage. However, it is one of the factors determining dosage together with the fluid or drug concentration and the size of the tubing.

So, why do nurses need to calculate IV drip rate? That’s what the next section is about.

2. Why Calculate IV Drip Rate

Depending on the medical equipment available in a hospital or health facility, drip fluids can be delivered by an IV infusion pump or by adjusting the gravity of fluid flow using a manual dial-a-flow or roller clamp.

As such, the reason for calculating the IV drip rate can vary depending on whether you use manual IV infusion or electronic pump infusion.

Manual infusion pumps are common in healthcare contexts where IV infusion pumps are not available for one reason or another. In this case, the nurse must calculate the drip rate to know how many drops of fluid the patient should receive each minute.

In most modern hospitals today, however, using electronic IV pumps is the typical way to deliver IV fluids. In this case, nurses set IV drip rate automatically using the pump interface. All they need to do is feed in the patient and prescription details and the drip rate is generated automatically.

Nonetheless, even when electronic IV pumps are used to deliver IV fluids, it is crucial that nurses know how to calculate the drip rate.

What for?

To verify that the automatically set IV pump drip rate is correct as per the prescription. This is especially necessary when infusing high-risk drugs.

So, exactly how do nurses calculate IV drip rate? The following section has the IV pump rate formula made easy for every nurse.
Calculating IV Drip Rate

3. How to Calculate IV Drip Rates

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Calculating IV Drip Rate

There are two key concepts nurses must understand as prerequisites to calculating IV drip rates.

  • gtt: An abbreviation for the Latin word “gutta” (Plural- “guttae”) meaning drop.
  • Infusion rate: The amount of fluid in mL delivered in one hour. The infusion rate is obtained by dividing the total fluid volume in mL by the number of infusion hours (mL/hr).
  • Drop factor: An IV tubing feature defined by the number of drops per milliliter (gtt/mL). IV tubing can be macro tubing or micro tubing.

Macro tubing (standard tubing) has a drip factor between 10 and 20. It is used with adults when delivering large fluid volumes at infusion rates of >80ml per hour. For example, if a tubing has a 20 gtt/mL drop factor, that translates to 20 guttae (drops) to make a milliliter of fluid.

Micro tubing has a drip factor of 60 gtt/ml and is used with neonatal and pediatric cases to deliver small fluid volumes.

To calculate IV drip rates, nurses need these three formula components:

  • Total fluid volume to be infused.
  • IV tubing drop factor.
  • Infusion time.

With all that in mind, here are the 3 steps to calculate IV drip rate:

  • Identify the type of IV tubing

Knowing the type of IV tubing is crucial to determining the correct drop factor to use in the IV drip rate formula. So, you need to find out if you are using the standard macro tubing or the specialized micro tubing.

  • Check/Calculate the drop factor

The IV tubing is already calibrated in gtt/ mL (drop factor). Once you identify the IV tubing for a patient’s infusion therapy, read the IV tubing drop factor on the package.

  • Calculate the IV drip rate

You obtain the IV drip rate using the formula: total fluid volume in ML divided by the infusion time in minutes, multiplied by the drop factor in gtt/mL.

In a simplified form:

Calculating IV Drip Rate

Since prescriptions may come written in hours for the infusion time and Liters for the infusion volume, it is important to keep in mind the standard conversions for these units:

  • 1000 mL = 1L
  • 60 min = 1 hour

So, let’s take an overall example for this step:

Assuming the doctor has prescribed 1liter of IV fluid to be infused over 10 hours using a macro tubing with a 10 gtt/mL drop factor. You will calculate the drip rate as follows:

  1. Convert 1L of IV fluid to milliliters = 1000mL (1 x 1000).
  2. Convert 10 hours to minutes = 600 minutes (60 x 10).
  3. Factor in IV tubing with a 10 gtt/mL drop factor

The drip rate for this fluid delivery will be:

Calculating IV Drip Rate
If you are wondering how to set the infusion pump rate and at what rate should the nurse set the infusion pump, I mentioned earlier that nurses only need to feed the patient and prescription details into the pump on the user interface.
Specifically:
  • Feed in patient weight (weight range).
  • Select infusion rate (mL/hr).
  • Select the total fluid volume to be infused (VTBI).
The infusion rate is set automatically.

However, once you do this, you can use the IV drip rate formula explained above to verify that it is exact.

4. Quick Summary

The IV pump rate formula determines the number of fluid drops a patient should receive in one minute or the drip rate.

The drip rate is calculated by dividing fluid volume (mL) by infusion time (minutes) and multiplying with the tubing drop factor (gtt/mL).

It’s crucial that every nurse knows how to calculate the drip rate, whether that serves to set a manual IV infusion device or to confirm the accuracy of an electronic IV pump setting.
Article by
Sara Alvarado
Greetings, I'm Sara, a dedicated nurse and a proud contributor to the AutoInfu blog. With my firsthand experience in the world of infusion pumps, I'm here to provide you with the latest insights, expert advice, and essential updates to ensure you stay informed about the infusion pump industry.

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