Drop Factor Chart: gtt/min by mL/hr and Tubing (10, 15, 20, 60)
Shows the work. Every example is computed with the formula and numbered steps. For study and exam practice, not for patient care.
For a gravity infusion you count drops, and how many drops make a milliliter depends on the tubing. The drop factor is printed on the tubing package.
Rule: gtt/min = mL/hr × drop factor ÷ 60. Equivalently, divide the mL/hr by the drop factor constant (60 ÷ drop factor). With 60 gtt/mL microdrip tubing the gtt/min equals the mL/hr.
For any other amount, use the IV drip rate (gtt/min) calculator: it shows the factor and each step.
Tubing types and the drop factor constant (60 ÷ drop factor)
| Drop factor | Tubing | Drops in 1 mL | Constant: divide mL/hr by |
|---|---|---|---|
| 10 gtt/mL | Macrodrip | 10 | 6 |
| 15 gtt/mL | Macrodrip | 15 | 4 |
| 20 gtt/mL | Macrodrip | 20 | 3 |
| 60 gtt/mL | Microdrip | 60 | 1 |
Drops per minute for an hourly volume, by drop factor (rounded to a whole drop)
| mL/hr | 10 gtt/mL | 15 gtt/mL | 20 gtt/mL | 60 gtt/mL |
|---|---|---|---|---|
| 10 | 2 | 3 | 3 | 10 |
| 20 | 3 | 5 | 7 | 20 |
| 25 | 4 | 6 | 8 | 25 |
| 30 | 5 | 8 | 10 | 30 |
| 50 | 8 | 13 | 17 | 50 |
| 60 | 10 | 15 | 20 | 60 |
| 75 | 13 | 19 | 25 | 75 |
| 80 | 13 | 20 | 27 | 80 |
| 100 | 17 | 25 | 33 | 100 |
| 120 | 20 | 30 | 40 | 120 |
| 125 | 21 | 31 | 42 | 125 |
| 150 | 25 | 38 | 50 | 150 |
| 175 | 29 | 44 | 58 | 175 |
| 200 | 33 | 50 | 67 | 200 |
| 250 | 42 | 63 | 83 | 250 |
Good to know
- A drop can't be split, so drip rates round to a whole number of drops per minute.
- Macrodrip tubing is usually 10, 15, or 20 gtt/mL; microdrip tubing is 60 gtt/mL. Always read the package: sets differ by manufacturer.
- For a time other than one hour, use the drip rate calculator: gtt/min = mL × drop factor ÷ minutes.
Worked example
Infuse 5% dextrose in water 500 mL IV over 2 hours by gravity. The tubing has a drop factor of 20 gtt/mL.
- Volume
- 500 mL
- Infusion time
- 120 minutes
- Drop factor
- 20 gtt/mL
Formula gtt/min = volume × drop factor ÷ minutes.
- gtt/min = volume × drop factor ÷ minutes.
- 500 mL × 20 gtt/mL ÷ 120 minutes = 83.33 gtt/min.
- A drop cannot be split, so round to a whole number: 83 gtt/min.
Answer 83 gtt/min
FAQ
What is a drop factor?
The number of drops (gtt) that make 1 mL with a given IV tubing set, printed on its package.
What drop factor is microdrip tubing?
60 gtt/mL. Macrodrip tubing is usually 10, 15, or 20 gtt/mL.
Terms on this page: Drop factor, gtt, Macrodrip, Microdrip
Sources
- Clinical Calculations: With Applications to General and Specialty Areas (Kee, Marshall, et al.) — Elsevier
- Calculate with Confidence (Morris) — Elsevier