Whenever you’re administering intravenous (IV) infusions, you need to know the flow rate, infusion time, and total volume. Fortunately, calculating any one of these three variables is easy to do when you know the other two variables. Use the following equations:
flow rate (mL/hr) = total volume (mL) ÷ infusion time (hr)
infusion time (hr) = total volume (mL) ÷ flow rate (mL/hr)
total volume (mL) = flow rate (mL/hr) × infusion time (hr)
For example, if you must administer 1 L (1,000 mL) of fluid over 4 hours, use the first formula to calculate the flow rate, like so:
flow rate (mL/hr) = total volume (mL) ÷ infusion time (hr)
flow rate (mL/hr) = 1,000 ÷ 4
flow rate (mL/hr) = 250
The flow rate is 250 mL/hr.