What is a drop factor?
The drop factor is the number of drops that make 1 mL with a specific IV administration set. It is printed on the tubing package and depends on the size of the opening in the drip chamber. You need it only for gravity infusions, to convert a volume per time into drops per minute.
Macrodrip and microdrip
| Tubing | Drop factor | Typical use |
|---|---|---|
| Macrodrip | 10, 15 or 20 gtt/mL | Large volumes and faster rates, for example 1,000 mL over 8 hours |
| Microdrip (minidrip) | 60 gtt/mL | Small volumes, slow rates, children and precise infusions |
The shortcut for microdrip
With 60 gtt/mL tubing, gtt/min equals mL/hr: 50 mL/hr is 50 gtt/min. The 60 drops per mL cancel the 60 minutes per hour.
Shortcuts also exist for macrodrip: divide mL/hr by 6 for 10 gtt/mL, by 4 for 15 gtt/mL, and by 3 for 20 gtt/mL.
Worked example
Infuse 500 mL over 4 hours with 20 gtt/mL tubing.
- mL/hr = 500 ÷ 4 = 125 mL/hr
- gtt/min = 500 × 20 ÷ 240 = 41.67
- = 42 gtt/min (shortcut: 125 ÷ 3 = 41.7)
Frequently asked questions
Where do you find the drop factor?
On the IV tubing package. It is not on the order.
What is the drop factor of microdrip tubing?
60 gtt/mL.