IV flow rate and drip rate calculations (mL/hr and gtt/min)
Two formulas cover most technician IV questions: volume ÷ time for mL/hr, and (volume × drop factor) ÷ minutes for gtt/min.
Method
- mL/hr = total volume (mL) ÷ time (hours).
- gtt/min = (volume in mL × drop factor in gtt/mL) ÷ time in minutes.
- Round drops per minute to a whole number. You cannot count part of a drop.
Worked examples
Example 1
Infuse 100 mL over 4 hours using tubing with a drop factor of 60 gtt/mL. What is the drip rate in gtt/min? Round to the nearest whole number.
Show solution
- gtt/min = (volume × drop factor) ÷ minutes
- = (100 mL × 60 gtt/mL) ÷ 240 min
- = 25 gtt/min
Answer: 25 gtt/min
Example 2
1,000 mL of normal saline is to be infused over 3 hours. What is the flow rate in mL/hr? Round to one decimal place.
Show solution
- Rate = volume ÷ time
- = 1,000 mL ÷ 3 hr
- = 333.3333 mL/hr, which rounds to 333.3 mL/hr
Answer: 333.3 mL/hr
Example 3
Infuse 1,000 mL over 10 hours using tubing with a drop factor of 15 gtt/mL. What is the drip rate in gtt/min? Round to the nearest whole number.
Show solution
- gtt/min = (volume × drop factor) ÷ minutes
- = (1,000 mL × 15 gtt/mL) ÷ 600 min
- = 25 gtt/min
Answer: 25 gtt/min
Tips
- Common drop factors are 10, 15 and 20 gtt/mL (macrodrip) and 60 gtt/mL (microdrip).
- With a 60 gtt/mL set, gtt/min equals mL/hr.
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