How to do gtt calculate gtt/min?

When calculating the drip rate, first identify which IV tubing you will be using, microdrip or macrodrip, so you can use the proper drop factor in your calculations. The drop factor is the number of drops in one mL of solution and is printed on the IV tubing package. Macrodrip and microdrip refers to the diameter of the needle where the drop enters the drip chamber. Macrodrip tubing generally delivers 10 to 20 gtt/mL and is used to infuse large volumes or to infuse fluids quickly. Microdrip tubing delivers 60 gtt/mL and is used for small or very precise amounts of fluid, as with neonates or pediatric patients.

If you simply need to figure out the infusion rate, or the mL per hour to infuse, take the total volume in mL, divided by the total time in hours that the medication is ordered to be infused over, to equal the rate in mL per hour. For example, if you have 1,000 mL Normal Saline to infuse over 8 hours, take 1,000 mL divided by 8 hours, to equal 125 mL/hr.

To calculate the drip rate, however, the drop factor is needed. The formula for calculating the IV drip rate is… total volume (in mL) divided by time (in minutes), multiplied by the drop factor (in gtt/mL), which equals the IV drip rate in gtt/min.

Let’s try an example.

The provider has ordered 1,000 mL Lactated Ringers to infuse over 8 hours. You have a macrodrip tubing with a drop factor of 15 gtt/mL. Calculate how many gtt/min to set as the IV flow rate. Using the formula, 1,000 mL divided by \(8\times 60\) (since we have 8 hours times 60min/hr), then multiply by 15 gtt/min to equal 31.2, rounded to 31 gtt/min.

Here’s a tip… When the IV tubing is microdrip, 60 gtt/mL, the drops per minute will be the same as the mL per hour. For example, you have 500 mL to infuse over 12 hours with a microdrip set. The total volume (500 mL), divided by the total time in hours (12), equals 41.6, rounded to 42 mL per hour.

The drops per minute would be calculated as total volume, divided by time (in minutes), multiplied by the drop factor of 60 gtts/min, which also equals 41.6, rounded to 42 drops per minute.

Let’s look at an example of an IV piggyback medication… 1 gram of Ancef in 100 mL of normal saline is to be infused over 30 minutes. You have macrodrip tubing with a drop factor of 10 gtt/mL. Calculate how many gtt/min to set as the IV drip rate. Use the formula, with 100 mL divided by 30 min, multiplied by 10 gtt/min, which equals 33.3, rounded to 33 gtt/min.

If you need to set this up on an IV infusion pump, use the formula, volume (mL) divided by time (min), multiplied by 60 min over 1 hour. This equals the IV flow rate in mL/hr which is the standard method of setting infusion rates on IV pumps. Using this formula, 100 mL divided by 30 min, times 60 min in 1 hr, equals 199.9, rounded to 200 mL/hr.

Once the infusion has started, monitor the rate closely to be sure it is infusing at the correct rate and check the patient’s IV site for signs of infiltration or inflammation.

• Order: 1000 mLof D5/W to infuse 130 mL /hr.
• Drop factor of tubing is 20 gtts = 1 mL.
• Formula:
• mL/hr X drop factor = gtt/min.
• 60 minutes.
• 130mL/hr x 20 gtt/min = 2600 = 43 gtt/min.

Drip rate (mL/hour) = Total volume (mL) / Infusion time

However, the drip rate can also be calculated using the drop rate formula (this function is available in the advanced mode of our gtt in min calculator):

Drip rate = Drops per hour / Drop factor,

or

Drip rate = (Drops per minute × 60) / Drop factor

It is crucial to set the drip rate very carefully! Even seemingly safe substances can have a potentially lethal effect on your patients - even the well-known and commonly used NaCl solution can lead to encephalopathy, seizures, and tetraplegia (paralysis of all four limbs). This effect is seen in patients with low sodium levels when the infusion rate is too fast.