Which formula correctly describes how to calculate IV infusion rate in mL/hour when given total volume and infusion time in hours?

Which formula correctly describes how to calculate IV infusion rate in mL/hour when given total volume and infusion time in hours?

• A. volume × time
• B. time ÷ volume
• C. volume ÷ time
• D. time ÷ volume × 2

Answer: (C)

Calculating the IV infusion rate relies on evenly distributing the total volume over the infusion time. The rate is the volume divided by the time, giving units of mL per hour when volume is in milliliters and time is in hours. So, if you have 1000 mL to infuse over 8 hours, the rate is 1000 ÷ 8 = 125 mL/hour. If the time increases, the rate decreases; if the time decreases, the rate increases, which matches the intuitive idea of spreading the same amount of fluid over a longer or shorter period. Other formulas don’t fit because they either produce the wrong units or give the inverse relationship. For example, multiplying volume by time yields a unit of mL·h, not a rate. Time divided by volume gives hours per milliliter, the inverse of the desired rate. The same idea applies to variations like adding a factor of 2.

Calculating the IV infusion rate relies on evenly distributing the total volume over the infusion time. The rate is the volume divided by the time, giving units of mL per hour when volume is in milliliters and time is in hours. So, if you have 1000 mL to infuse over 8 hours, the rate is 1000 ÷ 8 = 125 mL/hour. If the time increases, the rate decreases; if the time decreases, the rate increases, which matches the intuitive idea of spreading the same amount of fluid over a longer or shorter period.

Other formulas don’t fit because they either produce the wrong units or give the inverse relationship. For example, multiplying volume by time yields a unit of mL·h, not a rate. Time divided by volume gives hours per milliliter, the inverse of the desired rate. The same idea applies to variations like adding a factor of 2.