This free Dosage Calculations Practice Test #10 covers IV drip rates and infusion times: working out when an infusion will finish, the time left in a bag, counting drops to check a gravity line, gtt/min for short infusions, intake over a shift, 24-hour totals with piggybacks, when to start an infusion, and what to do when an IV falls behind. Work through 10 timed questions, then check every answer with the full rationales below. No sign-up required.
All 10 Questions With Answers & Rationales
Prefer to work at your own pace? Every question from the timed quiz above is listed here in full. Choose your answer, then tap Show Answer & Rationale to check it.
Question 1: Infusion end time
A client's 1,000 mL bag of normal saline is started at 0730 on an infusion pump at 80 mL/hr. At what time will the infusion finish?
- A. 1930
- B. 2000
- C. 2030
- D. 1730
Show Answer & Rationale
Answer: B. 2000
Rationale: Infusion time = total volume ÷ rate: 1,000 mL ÷ 80 mL/hr = 12.5 hours, which is 12 hours 30 minutes. 0730 + 12 hours = 1930, plus 30 minutes = 2000. 1930 drops the half hour, a common error when 12.5 is read as 12 hours. 2030 rounds 12.5 up to 13 hours; never round infusion time to a whole hour. 1730 is a counting error (10 hours). Convert the decimal part of an hour to minutes by multiplying by 60 (0.5 × 60 = 30 minutes).
Question 2: Time left in the bag
At 1015 the nurse notes 450 mL left in a bag of lactated Ringer's that is infusing by pump at 100 mL/hr. At what time will the bag be empty?
- A. 1445
- B. 1415
- C. 1515
- D. 1345
Show Answer & Rationale
Answer: A. 1445
Rationale: Use the volume that remains, not the original bag size: 450 mL ÷ 100 mL/hr = 4.5 hours = 4 hours 30 minutes. 1015 + 4 hours = 1415, plus 30 minutes = 1445. 1415 leaves out the 30 minutes. 1515 adds 5 hours. 1345 subtracts instead of adding. Knowing when a bag will run dry lets the nurse have the next bag or the next prescription ready so the line does not run empty or clot.
Question 3: gtt/min for a short infusion
No pump is available. A client is to receive 50 mL of an IV medication over 20 minutes by gravity. The tubing drop factor is 10 gtt/mL. At how many drops per minute should the nurse set the infusion?
- A. 150 gtt/min
- B. 2.5 gtt/min
- C. 25 gtt/min
- D. 500 gtt/min
Show Answer & Rationale
Answer: C. 25 gtt/min
Rationale: gtt/min = (volume in mL × drop factor) ÷ time in minutes = (50 × 10) ÷ 20 = 500 ÷ 20 = 25 gtt/min. When the time is already in minutes, do not convert to hours. 150 is the rate in mL/hr (50 mL ÷ 20 min × 60), not drops per minute. 2.5 forgets the drop factor (50 ÷ 20). 500 is the total number of drops, never divided by time. Always check that the drop factor on the tubing package matches the number you use, because tubing sets differ.
Question 4: Counting drops to check a gravity IV
A client has a gravity IV with tubing that has a drop factor of 20 gtt/mL. The nurse counts 10 drops in the drip chamber in 15 seconds. About how many mL/hr is the client receiving?
- A. 40 mL/hr
- B. 30 mL/hr
- C. 2 mL/hr
- D. 120 mL/hr
Show Answer & Rationale
Answer: D. 120 mL/hr
Rationale: First find drops per minute: 10 drops in 15 seconds × 4 = 40 gtt/min. Convert to mL per minute: 40 gtt/min ÷ 20 gtt/mL = 2 mL/min. Convert to mL/hr: 2 mL/min × 60 = 120 mL/hr. 40 mL/hr confuses gtt/min with mL/hr. 30 mL/hr treats the 10 drops as a full minute's count. 2 mL/hr stops at mL per minute and labels it per hour. Counting for 15 seconds and multiplying by 4 is quick, but a full 60-second count is more accurate; compare the result with the prescribed rate and adjust the roller clamp if needed.
Question 5: How long a gravity IV will take
A 500 mL bag is infusing by gravity at 25 gtt/min. The tubing drop factor is 15 gtt/mL. How long will the bag take to infuse?
- A. 5 hours
- B. 20 hours
- C. 13 hours 53 minutes
- D. 8 hours 20 minutes
Show Answer & Rationale
Answer: A. 5 hours
Rationale: Convert drops to mL: 25 gtt/min ÷ 15 gtt/mL = 1.67 mL/min, which is 100 mL/hr (1.67 × 60). Time = 500 mL ÷ 100 mL/hr = 5 hours. Another way: total drops = 500 mL × 15 = 7,500 gtt; 7,500 ÷ 25 gtt/min = 300 minutes = 5 hours. 20 hours divides 500 by 25 and ignores the drop factor. 13 hours 53 minutes comes from multiplying by 25 and dividing by 15 (the formula upside down). 8 hours 20 minutes is 500 ÷ 60, which mixes up minutes and mL.
Question 6: An IV that has fallen behind
A client has 1,000 mL of IV fluid prescribed over 8 hours, set at 125 mL/hr. Four hours later 650 mL remain in the bag instead of the expected 500 mL. What should the nurse do first?
- A. Increase the rate to 250 mL/hr for one hour to catch up
- B. Increase the rate to 163 mL/hr so the bag finishes on time
- C. Assess the client and the IV site, then follow facility policy or contact the prescriber before changing the rate
- D. Leave the rate unchanged and document the difference at the end of the shift
Show Answer & Rationale
Answer: C. Assess the client and the IV site, then follow facility policy or contact the prescriber before changing the rate
Rationale: Finishing on time would need 650 mL ÷ 4 hours = 162.5 mL/hr, about a 30% increase over 125 mL/hr. Before any change the nurse assesses the client (lung sounds, edema, intake and output, vital signs) and checks the IV site and tubing for infiltration, kinks or a closed clamp, because the cause matters. Whether a nurse may recalculate the rate, and by how much, is set by facility policy; many policies allow only a small adjustment and require the prescriber for anything larger. Never 'catch up' with a large increase such as 250 mL/hr: it can cause fluid overload, especially in older adults and clients with heart or kidney disease. Ignoring the problem until the end of the shift lets the client go without fluid that was prescribed.
Question 7: Volume infused over a shift
An IV infuses by pump at 90 mL/hr from 1900 to 0700. The infusion was paused for 45 minutes during the night while the client went to imaging. How much IV fluid should the nurse record as intake for the shift?
- A. 1,080 mL
- B. 1,012.5 mL
- C. 1,035 mL
- D. 945 mL
Show Answer & Rationale
Answer: B. 1,012.5 mL
Rationale: 1900 to 0700 is 12 hours. Subtract the 45-minute pause: 12 − 0.75 = 11.25 hours of infusion. Volume = 90 mL/hr × 11.25 hours = 1,012.5 mL. 1,080 mL ignores the pause (90 × 12). 1,035 mL subtracts 45 mL instead of 45 minutes of fluid. 945 mL subtracts 1.5 hours. Always check the pump's volume-infused display as well; it is the most reliable record and should match your calculation closely.
Question 8: Gravity rate and end time across midnight
At 2130 the nurse hangs 750 mL of IV fluid prescribed over 6 hours. It will run by gravity with tubing that has a drop factor of 20 gtt/mL. Which drip rate and finish time are correct?
- A. 125 gtt/min; finishes at 0330
- B. 42 gtt/min; finishes at 1530
- C. 31 gtt/min; finishes at 0330
- D. 42 gtt/min; finishes at 0330
Show Answer & Rationale
Answer: D. 42 gtt/min; finishes at 0330
Rationale: gtt/min = (750 mL × 20 gtt/mL) ÷ (6 × 60 minutes) = 15,000 ÷ 360 = 41.7, rounded to 42 gtt/min (you cannot count part of a drop). Finish time: 2130 + 6 hours crosses midnight, so the answer is 0330 the next morning. 125 is the rate in mL/hr (750 ÷ 6), not drops. 31 gtt/min uses a drop factor of 15 instead of the 20 on the tubing. 1530 adds the hours on the wrong side of the 24-hour clock.
Question 9: 24-hour total with piggybacks
A primary IV runs at 100 mL/hr. An IV piggyback of 50 mL is given over 30 minutes every 6 hours, and the pump pauses the primary infusion while each piggyback runs. What is the client's total IV intake for 24 hours?
- A. 2,600 mL
- B. 2,400 mL
- C. 2,200 mL
- D. 2,300 mL
Show Answer & Rationale
Answer: B. 2,400 mL
Rationale: Every 6 hours means 4 piggybacks in 24 hours: 4 × 50 mL = 200 mL. The primary is paused 30 minutes each time: 4 × 0.5 = 2 hours, so it runs 22 hours × 100 mL/hr = 2,200 mL. Total = 2,200 + 200 = 2,400 mL. 2,600 mL forgets that the primary was paused (2,400 + 200). 2,200 mL leaves out the piggybacks. 2,300 mL counts only two piggybacks. Pumps differ in how they run secondary infusions, so confirm the setup on your own pump.
Question 10: Start time and rate to finish on time
A prescription reads: give 100 mL of an IV medication over 45 minutes, to be completed by 0800. What is the latest time the nurse can start the infusion, and at what rate should the pump be set?
- A. Start at 0700 at 100 mL/hr
- B. Start at 0715 at 75 mL/hr
- C. Start at 0715 at 133 mL/hr
- D. Start at 0745 at 133 mL/hr
Show Answer & Rationale
Answer: C. Start at 0715 at 133 mL/hr
Rationale: Rate: 45 minutes = 0.75 hour, so 100 mL ÷ 0.75 hr = 133.3 mL/hr (133 mL/hr, or 133.3 if your pump programs tenths). Or: 100 mL ÷ 45 min × 60 = 133.3 mL/hr. Latest start: 0800 − 45 minutes = 0715. 100 mL/hr from 0700 treats 45 minutes as an hour. 75 mL/hr comes from 100 × 0.75, multiplying where you should divide. 0745 starts only 15 minutes before the deadline, so the infusion would finish at 0830. Many pumps let you enter the volume and time and calculate the rate, but always check that the rate makes sense.
Dosage Calculations Practice Tests
Master the medication math that shows up most on the NCLEX with free, timed dosage questions, complete with answers and step-by-step rationales. New tests are added to this series regularly.
Dosage Calculations Practice Questions
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