Regardless of the method, you will be responsible for calculating the correct IV flow rate. Example: The provider has ordered 1,000 mL 0.9% sodium chloride to infuse over 8 hr. You have a macrodrip tubing with a drop factor of 15 gtt/mL available. Calculate how many gtt/min to set as the IV flow rate. Step 1: Choose the formula. Step 2: Use the formula. Example: The provider has ordered ranitidine (Zantac) 50 mg in 100 mL 0.9% sodium chloride intravenous piggyback to be infused over 20 min.