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 600 mL of 5% dextrose in water to infuse over 8 hr. Determine how many mL/hr to set the IV pump to deliver. Step 1: Choose the formula. Step 2: Use the formula. When calculating the flow rate, first determine whether the intravenous tubing you are using is microdrip or macrodrip, so that you can use the appropriate drop factor in your calculations.