Drop Factor (gtt/mL): Definition and How to Use It
Shows the work. Every example is computed with the formula and numbered steps. For study and exam practice, not for patient care.
Drop factor: The number of drops (gtt) that make 1 mL with a given IV tubing set, printed on the tubing package.
The drop factor tells you how many drops of fluid make one milliliter with a particular IV administration set. It is printed on the tubing package, written in gtt/mL. Different tubing makes different-sized drops, so the same mL/hr gives a different number of drops per minute.
You need the drop factor only for a gravity infusion, where you count drops. An infusion pump is set in mL/hr and doesn’t use it.
The drip rate formula: gtt/min = volume (mL) × drop factor ÷ time (minutes). An exam question gives the drop factor; in practice, read it from the package of the tubing you hang.
Order: levofloxacin 250 mg in 50 mL IV over 60 minutes. The secondary tubing has a drop factor of 15 gtt/mL.
- Volume
- 50 mL
- Infusion time
- 60 minutes
- Drop factor
- 15 gtt/mL
Formula gtt/min = volume × drop factor ÷ minutes.
- gtt/min = volume × drop factor ÷ minutes.
- 50 mL × 15 gtt/mL ÷ 60 minutes = 12.5 gtt/min.
- A drop cannot be split, so round to a whole number: 13 gtt/min.
Answer 13 gtt/min
The drop factor chart lists drops per minute for common hourly rates with each tubing.
Sources
- Clinical Calculations: With Applications to General and Specialty Areas — Elsevier (Kee, Marshall, et al.)
- Calculate with Confidence — Elsevier (Morris)