Infusion Drip Rate Formula
Given a certain amount of liquid, a time period, and a drop factor (gtts/mL), what is the necessary IV flow rate in gtts/min?
This measurement is used when the IV is regulated manually. Because it is not possible to give a patient a fraction of a drop, it is typical to round answers for these problems up or down to the nearest whole number.
Formula:
Example: Calculate the IV flow rate for 1200 mL of NS to be infused in 6 hours. The infusion set is calibrated for a drop factor of 15 gtts/mL.

x Drop Factor (gtts/mL) = Y (Flow Rate in gtts/min) 
Convert 6 hours to minutes.
 min ← hr ( x by 60 )
 6 hr x 60 = 360 min

x 15 gtts/mL = 50 gtts/min 
Example: Calculate the IV flow rate for 200 mL of 0.9% NaCl IV over 120 minutes. Infusion set has drop factor of 20 gtts/mL.

x Drop Factor (gtts/mL) = Y (Flow Rate in gtts/min) 

x 20 gtts/mL = 33 gtts/min 