Drop factor (on the tubing package)
31 gtt/min
Always check the order, the tubing's drop factor and your facility's policy. Recount the drops for a full minute after you set the rate. Reviewed September 30, 2026.
Drip rate formula
gtt/min = volume (mL) × drop factor (gtt/mL)time (minutes)
mL/hr = volume (mL)time (hours)
Use the first formula when the fluid runs by gravity and you regulate it with the roller clamp. Use the second when an infusion pump controls the rate. If the time is in hours, multiply the hours by 60 before you divide. Round drops per minute to the nearest whole number.
Drop factors: macrodrip vs microdrip
| Tubing | Drop factor | Typical use |
|---|---|---|
| Macrodrip | 10, 15 or 20 gtt/mL | General IV fluids for adults, larger volumes and faster rates |
| Microdrip | 60 gtt/mL | Small volumes and slow rates where precision matters, such as infants and children |
The drop factor depends on the manufacturer. Read it on the tubing package every time; do not assume it is the same as the last bag.
Worked examples
1. Gravity, macrodrip
Order: 1,000 mL normal saline over 8 hours. Tubing: 15 gtt/mL.
8 hours × 60 = 480 minutes. 1,000 × 15 ÷ 480 = 31.25. Set 31 gtt/min.
2. Gravity, microdrip
Order: 250 mL over 5 hours. Tubing: 60 gtt/mL.
250 × 60 ÷ 300 = 50 gtt/min. With microdrip tubing this equals the mL/hr rate (250 ÷ 5 = 50 mL/hr).
3. Short infusion
Order: 100 mL IV piggyback over 30 minutes. Tubing: 20 gtt/mL.
100 × 20 ÷ 30 = 66.7. Set 67 gtt/min. On a pump: 100 mL ÷ 0.5 hr = 200 mL/hr.
4. Pump rate
Order: 500 mL over 6 hours on a pump.
500 ÷ 6 = 83.3. Program 83 mL/hr (or 83.3 if your pump and policy allow decimals).
Drip rate chart for common orders
Drops per minute, rounded to the nearest whole drop.
| Order | mL/hr | 10 gtt/mL | 15 gtt/mL | 20 gtt/mL | 60 gtt/mL |
|---|---|---|---|---|---|
| 1,000 mL over 8 hr | 125 | 21 | 31 | 42 | 125 |
| 1,000 mL over 12 hr | 83.3 | 14 | 21 | 28 | 83 |
| 500 mL over 4 hr | 125 | 21 | 31 | 42 | 125 |
| 250 mL over 2 hr | 125 | 21 | 31 | 42 | 125 |
| 100 mL over 30 min | 200 | 33 | 50 | 67 | 200 |
How to set a gravity drip rate
- Check the order: fluid or medication, volume, time or rate, and the patient.
- Read the drop factor on the tubing package and calculate gtt/min.
- Prime the tubing, connect it and open the roller clamp slowly.
- Count the drops in the drip chamber for 15 seconds and multiply by 4, then adjust the clamp until you reach the target.
- Recount for a full minute, label the bag with the start time, and check the rate and the site often, since position changes can alter a gravity flow.
Frequently asked questions
What is the IV drip rate formula?
Drops per minute (gtt/min) = total volume (mL) × drop factor (gtt/mL) ÷ time (minutes). Round the answer to the nearest whole drop, because you cannot count part of a drop.
What is a drop factor?
The drop factor is the number of drops that make 1 mL with a given IV tubing. It is printed on the tubing package. Macrodrip tubing is usually 10, 15 or 20 gtt/mL; microdrip tubing is 60 gtt/mL.
How do I calculate mL per hour?
mL/hr = total volume (mL) ÷ time (hours). For example, 1,000 mL over 8 hours runs at 125 mL/hr. This is the number you program into an infusion pump.
Why is gtt/min the same as mL/hr with microdrip tubing?
Microdrip tubing delivers 60 drops per mL, and there are 60 minutes in an hour. The two 60s cancel out, so a rate of 50 mL/hr runs at 50 gtt/min.
Should I round mL/hr?
Most adult pumps accept whole numbers or one decimal place. Follow your pump and facility policy. For gravity infusions, always round drops per minute to a whole number.
How long will an infusion take?
Time (hours) = volume (mL) ÷ rate (mL/hr). Use the third tab of the calculator to get the time and the expected finish time.
More tools
Sources: Open RN, Nursing Skills 5.14: IV Infusion by Gravity · WisTech Open, Nursing Dosage Calculations: IV Flow Rates and Infusion Time. Examples written by our editorial team. Reviewed September 30, 2026.