Set 8 of 10 · IV drip rate
IV Drip Rate Calculation Practice: Drops per Minute (gtt/min)
When an IV runs by gravity, without a pump, the nurse sets the rate by counting drops in the drip chamber and adjusting the roller clamp. The target is in drops per minute (gtt/min). The practice questions on this page are free, with no sign-up.
The drop factor, printed on the tubing package, says how many drops make 1 mL. Macrodrip tubing is commonly 10, 15 or 20 gtt/mL; microdrip tubing is 60 gtt/mL.
IV drip rate formula: drops per minute (gtt/min)
- Drip rate
- gtt/min = volume (mL) × drop factor (gtt/mL) ÷ time (min)
- From an hourly rate
- gtt/min = mL/hr × drop factor ÷ 60
- Microdrip shortcut
- with 60 gtt/mL tubing, gtt/min = mL/hr
- Work from the unrounded volume and time, not from an mL/hr rate you have already rounded.
- Read the drop factor from the tubing package every time. The same order gives a different drip rate with different tubing.
- Count the drops for a full minute while you adjust the roller clamp, then recheck, because a gravity rate can drift.
Worked example: drip rate calculation
1,000 mL of lactated Ringer's is prescribed to infuse over 8 hours by gravity. The tubing drop factor is 20 gtt/mL. How many gtt/min will the nurse count? Round to the nearest whole number.
- Change hours to minutes: 8 hr × 60 = 480 min.
- Set up: (1,000 mL × 20 gtt/mL) ÷ 480 min = 20,000 ÷ 480.
- Solve: 41.667 gtt/min.
- Round: you can't count part of a drop, so drip rates are rounded to the nearest whole number: 42 gtt/min.
Answer: 42 gtt/min
Practice this set on the exam screen
The set opens in the NCLEX-style test interface. Type each answer, submit it to see the correct answer and its worked rationale, then move on. Your progress is saved in this browser, and the last screen shows your score.
Answer key
IV drip rate practice questions: answers and rationales
Try the questions first. Open one to read its answer and rationale.
Question 1A 31-year-old client at an urgent care clinic is prescribed 500 mL of 0.9% sodium chloride IV to infuse over 4 hours by gravity. The tubing has a drop factor of 15 gtt/mL. How many gtt/min will the nurse set? Round to the nearest whole number. Record your answer as a whole number.
Drip rate = volume × drop factor ÷ time in minutes. Change the time: 4 hr × 60 = 240 min. Then (500 mL × 15 gtt/mL) ÷ 240 min = 7,500 ÷ 240 = 31.25 gtt/min. Part of a drop cannot be counted, so the answer is rounded to the nearest whole number: 31 gtt/min. Common errors: dividing by 4 instead of 240, which gives 1,875, or leaving out the drop factor, which gives about 2 mL/min rather than a drip rate. The nurse counts the drops for a full minute while adjusting the roller clamp. Takeaway: gtt/min = mL × drop factor ÷ minutes; change hours to minutes first.
Sources: Open RN Nursing Skills (ACC adaptation), 5.14 IV Infusion by Gravity; Open RN Nursing Skills (ACC adaptation), 5.5 Rounding
Question 2An 84-year-old resident of a long-term care facility is prescribed dextrose 5% in 0.45% sodium chloride IV at 50 mL/hr by gravity. The nurse uses microdrip tubing with a drop factor of 60 gtt/mL. How many gtt/min will the nurse set? Round to the nearest whole number. Record your answer as a whole number.
From an hourly rate, gtt/min = mL/hr × drop factor ÷ 60. Here: 50 mL/hr × 60 gtt/mL ÷ 60 min/hr = 50 gtt/min. The two 60s cancel, so with microdrip tubing the drip rate in gtt/min always equals the rate in mL/hr. Common error: stopping at 50 × 60 = 3,000, which is drops per hour, not per minute. With 15 gtt/mL macrodrip tubing the same prescription would need only 12.5, or about 13 gtt/min, so the drop factor on the tubing package must be read every time. Takeaway: with 60 gtt/mL tubing, gtt/min equals mL/hr.
Sources: Open RN Nursing Skills (ACC adaptation), 5.14 IV Infusion by Gravity; Open RN Nursing Skills (ACC adaptation), 5.4 Equivalencies
Question 3A 55-year-old client receiving home health care is prescribed ceftriaxone 1 g IV once daily. Each dose is supplied in 50 mL of 0.9% sodium chloride to infuse over 30 minutes by gravity. The tubing has a drop factor of 20 gtt/mL. How many gtt/min will the nurse set? Round to the nearest whole number. Record your answer as a whole number.
The time is already in minutes, so use it directly: gtt/min = volume × drop factor ÷ minutes. (50 mL × 20 gtt/mL) ÷ 30 min = 1,000 ÷ 30 = 33.33 gtt/min, rounded to 33 gtt/min. The 1 g dose is not part of the calculation; the drip rate depends on the volume, the tubing and the time. Common errors: dividing by 60 out of habit (about 17 gtt/min, which would take an hour), or using the drop factor of different tubing. Check: 33 gtt/min ÷ 20 gtt/mL = 1.65 mL/min, and 1.65 mL/min × 30 min is about 50 mL. Takeaway: for a short infusion, divide by the minutes given; the 60 is used only when the time is in hours.
Sources: Open RN Nursing Skills (ACC adaptation), 5.14 IV Infusion by Gravity; DailyMed: Ceftriaxone for Injection label (IM and IV reconstitution tables; adult and pediatric dosage; infuse over 30 minutes)
Question 4A 48-year-old client on a medical unit is prescribed dextrose 5% in water IV at 125 mL/hr by gravity. The tubing has a drop factor of 15 gtt/mL. During rounds, the nurse counts 28 gtt/min in the drip chamber. How many mL/hr is the client receiving at this drip rate? Round to the nearest tenth. Record your answer using 1 decimal place.
Work backward from the drip rate. Drops per hour: 28 gtt/min × 60 min/hr = 1,680 gtt/hr. Volume per hour: 1,680 gtt/hr ÷ 15 gtt/mL = 112 mL/hr. The client is receiving 112 mL/hr, less than the 125 mL/hr prescribed. The prescribed rate needs 125 mL/hr × 15 gtt/mL ÷ 60 = 31.25, or 31 gtt/min, so the nurse adjusts the roller clamp and counts again. Common error: multiplying by the drop factor instead of dividing (28 × 15 = 420), which treats drops as if they were mL. A gravity rate can drift, so it is rechecked regularly. Takeaway: mL/hr = gtt/min × 60 ÷ drop factor.
Sources: Open RN Nursing Skills (ACC adaptation), 5.14 IV Infusion by Gravity; StatPearls: Dose Calculation Dimensional Analysis Factor-Label Method
Question 5A 70-year-old client on a surgical unit is prescribed 1.5 L of lactated Ringer's IV to infuse over 12 hours by gravity. The infusion has been running at 31 gtt/min through tubing with a drop factor of 15 gtt/mL. The nurse replaces the tubing with a set that has a drop factor of 10 gtt/mL. How many gtt/min will the nurse set with the new tubing? Round to the nearest whole number. Record your answer as a whole number.
The prescription has not changed, so recalculate from the volume and time with the new drop factor. Volume: 1.5 L × 1,000 = 1,500 mL. Time: 12 hr × 60 = 720 min. Drip rate: (1,500 mL × 10 gtt/mL) ÷ 720 min = 15,000 ÷ 720 = 20.83 gtt/min, rounded to 21 gtt/min. Keeping the old 31 gtt/min with 10 gtt/mL tubing would deliver 186 mL/hr instead of 125 mL/hr, because each drop is now larger. Common errors: leaving the volume as 1.5, or using the old drop factor of 15. Takeaway: the same prescription needs a different drip rate with different tubing, so recalculate whenever the drop factor changes.
Sources: Open RN Nursing Skills (ACC adaptation), 5.14 IV Infusion by Gravity; Open RN Nursing Skills (ACC adaptation), 5.4 Equivalencies
FAQ
Drip rate calculation: FAQ
How to calculate drops per minute?
What is the drip rate for 100 mL over 30 minutes?
How do I calculate the drip rate for 1,000 mL of 0.9% sodium chloride over 8 hours?
Sources: Open RN Nursing Skills (ACC adaptation), 5.14 IV Infusion by Gravity; Open RN Nursing Skills (ACC adaptation), 5.5 Rounding; Open RN Nursing Skills (ACC adaptation), 5.4 Equivalencies