How To Calculate IV Drip Rates

How To Calculate IV Drip Rates


Before we begin, in order to calculate drip rates, you will need to know how to calculate flow rates. For more information on how to calculate flow rates, click here. Also, what even is a drip rate? When nurses are required to use gravity tubing to run an IV, they are basically infusing an IV fluid without an electronic pump that controls the rate at which the fluid is infused. The benefits of doing it this way include the fact that you don’t need a pump, faster to set up, and it takes up less space. The down side of gravity transfusions is that they are less precise than using pumps, more dangerous and harder for beginners to master. Over 95% of floors use purely electronic IV pumps purely because of their safety. Some units still use gravity infusions for basic, “safe” medications. Hospitals often have policies that forbid medications such as Potassium from being infused through gravity infusions because of their high risk of harm if given at the wrong rate. An electronic IV pump will tell you exactly how fast it is infusing. If gravity infusions only consist of a bag, a line and an access port to the patient, how do you know how fast the fluid is infusing? That is why we calculate drip rates. Drip rates are how many drips of fluid you see falling through a chamber in one minute. Based on this number, we can see how fast it is actually infusing. Don’t be confused, here is how you do it.

The Formula (The 3 Step Method)

The formula for how to how to calculate drip rates using this easy method is as follows:

Part 1: The Flow Rate

The Flow Rate is simply how many millilitres per hour is the fluid supposed to me infusing. It is unique to every question. In order to calculate this, divide the volume to be infused in millilitres by the time in hours. Click here for a more in-depth tutorial. In some questions the flow rate is given to you, in some questions you need to calculate the flow rate before you calculate the drip rate.

Part 2: The Drop Factor

What is a drop factor? A drop factor, also known as a drip factor, is a measurement used to determine how many drips of fluid are needed for the particular tubing being used to add up to 1ml. This is also unique to every question because different size tubing results in a different number of drops being required to add up to 1 ml. Thicker tubing requires less drips because the drops are bigger. Thinner tubing requires more drips to add up to 1ml because the drops are smaller. In each drip rate question, the “Drop Factor” of the tubing must be given to you in order to be able to calculate the question. The unit for drop factors is gtt/minute (gtt = drop).

Part 3: The Time Conversion

The time conversion is unique to this method of calculating drip rates. It is basically a way of cancelling units out in order to get the correct result. The time conversion will always be 1 hour/60 minutes for every question you do.

The Answer

The answer is obviously the desired drip rate. The desired drip rate describes how man drips per minute you are going to count falling through the drip chamber in order to have the correct speed of infusion.

Let’s try a practice question in order to learn how to apply this formula.

Practice Question

The Physician orders and IV infusion of D5W 1000ml to infuse over the next 8 hours. The IV tubing that you are using delivers 15gtt/ml. What is the correct drip rate?

Part One: Flow Rate

The flow rate in this question needs to be calculated as a flow rate in ml/hour is not given. In order to do this, we divide 1000ml by 8 hours. This gives us: 125ml/hour

Part Two: Drop Factor

The drop factor in this question is 15gtt/ml. The question will always tell you what the drop factor is as it can vary.

Part Three: Time Conversion.

The time conversion part of this equation is always 1 hour/60 minutes. All the time, every time.

Solve The Equation

Now that you have all of the parts for the formula, its time plug all 3 parts in and solve. It should look like this when you are complete. The red markings indicate the units that cancel out. In order to solve, you just multiply the top row across and the bottom row across.

Simplify The Answer

In order to set a flow rate in the real world, there is no way any nurse on the face of this planet has time to wait for 60 minutes in order to count 1875 drops in order to ensure that the drip rate is correct. In order to simplify this, simply divide by 60.

Round the Answer

Unless you are a super human, there is no way to be able to see 1 quarter of a drip. In order to solve this, round to the nearest whole number. In this case, it would be 31 gtt per minute.

Congratulations, you now know how to calculate IV drip rates! Try these practice questions to see if you learned anything!

1. 960ml of D5W needs to be infused over 24 hours. No electronic pumps are available. The drop factor is 15 gtt/ml. What is the drip rate?

2. 1200 ml of normal saline needs to be infused over 8 hours through gravity infusion. The drop factor of the tubing is 60 gtt per minute.

3. 2g of Ancef in a 240 ml bag needs to be infused in 12 hours. IV tubing has a drop factor of 60gtt/ml. What is the drip rate?

4. 900ml of NS needs to be given in 4 hours. Drop factor is 20. What is the drip rate?

5. A 60ml mini bag with IV rocephin needs to be infused over 2 hours. The drop factor is 60. What is the drop rate in drips per minute?

6. 840ml of 2/3 and 1/3 needs to be infused over 10 hours. The drop factor of the tubing you are using is 20 gtt/ml. What is the drip rate in gtt/min?

7. The physician tells you to infuse 240ml of NS over 2 hours. The drop factor is 60. What is the drip rate in gtt/min?

8. 1gm Rocephin needs to be given in a 90ml bag over 45 minutes. With a drop factor of 20, how many drips per minute will you see in the drip chamber?

9. A patient requires 960ml of normal saline because they are severely dehydrated. The infusion is scheduled to take 16 hours the drop factor is 20. What is the drip rate in gtt/min?

10. 30ml needs to be infused over 30 minutes. The drop factor is 15gtt/ml. What is the drip rate in gtt/min?

11. 500 mL of Normal Saline with 10 meq of potassium chloride to infuse over 5 hours. The drip factor is 10 drips per ml. What is the drip rate?

12. 1gm of Ancef in 300ml are to infuse over 40 minutes. the drip factor is 20 gtt/mL. What is the drip rate?

13. 400ml of Normal Saline are to infuse over 3 hours. The drip factor is 10 drips per ml. What is the drip rate?

14. 2L of Normal Saline are to infuse over 48 hours. The drip factor is 15 gtt/mL. What is the drip rate?

15. 1500 mL of Lactated Ringer’s needs to be infused over 12 hours. The drip factor is 15 gtt/mL. What is the drip rate?