Which statement best describes how the IV flow rate in mL/hr is calculated?

• A. mL/hr = total volume (mL) divided by time (hours)
• B. mL/hr = total volume (mL) times time (hours)
• C. mL/hr = time (hours) divided by total volume (mL)
• D. mL/hr = total volume (mL) minus time (hours)

Answer: (D)

Flow rate is how many milliliters pass in one hour. The calculation uses total volume to be infused divided by the infusion time in hours, giving mL per hour. For example, 1000 mL over 8 hours equals 125 mL/hr. If time is given in minutes, convert to hours first (minutes ÷ 60). The other ways don’t represent a rate: multiplying volume by time changes the units; dividing time by volume would yield hours per milliliter; subtracting time from volume has no meaning for flow rate.