Med Math: Drop Factors Question #14


The order for 500 mL of 0.45 NS will infuse over 8 hours at 63 mL/hr. The IV infusion set available has a gtt factor of 15 mL. Calculate gtts per minute.


  1. 40 gtt/min
    • Rationale:
  2. 23 gtt/min
    • Rationale:
  3. 16 gtt/min
    • Rationale:
  4. 22 gtt/min
    • Rationale:



NS or Normal Saline is ordered at 500 ml. The 0.45 NS and the 63 ml/hr is extra information and not needed to solve the problem. You would need to know how much volume you needed in order to solve. The volume is 500 ml over 8 hour. The hour is converted to minutes in the second step of the problem. The Drop factor is also noted to be the gtt factor and is 15 ml. There is a simple formula below for calculating the gtt/min. The final answer should have gtt/min within and rounded to the nearest whole number.

Total ML

—– x gtt factor


Answer divided by 60= ___gtt/min
See the formula in action below….

500 ml

——— x 15 ml DF= __937.5____ml

8 hours

937.5 / 60 = _15.625 round= 16 gtt/min_

Learning Outcomes

Test Taking Tip

Video Rationale