Calculate drops per minute and mL per hour for IV infusions
IV Rate Formulas
mL per hour = Total volume (mL) ÷ Time (hours)
Drops per minute = (Volume in mL × Drop factor) ÷ Time in minutes
Drop factor is the number of drops per mL — it depends on the tubing set.
Common drop factors: 10 gtt/mL (macro), 15 gtt/mL (macro), 20 gtt/mL (macro), 60 gtt/mL (micro).
Examples
Infuse 1,000 mL over 8 hours. What is the rate in mL/hr?
1,000 mL ÷ 8 hours = 125 mL/hr
Infuse 500 mL over 4 hours with a 15 gtt/mL set. What is the drip rate?
With a 60 gtt/mL (micro drip) set, the drops per minute equals the mL per hour. If the order is 125 mL/hr, set the drip to 125 gtt/min. No calculation needed.
💡 Always round drip rates to the nearest whole number — you can't count half a drop. And double-check: does the rate seem reasonable? Most adult IVs run between 20–150 gtt/min.
🎯 Practice Problems
1. Infuse 1,000 mL over 10 hours. What is the rate in mL/hr?
A) 10 mL/hr
B) 50 mL/hr
C) 100 mL/hr
D) 1,000 mL/hr
2. Order: 250 mL over 2 hours. Drop factor: 20 gtt/mL. What is the drip rate?
A) 21 gtt/min
B) 42 gtt/min
C) 83 gtt/min
D) 125 gtt/min
3. A 60 gtt/mL micro drip is set to run at 75 mL/hr. What is the drip rate in gtt/min?
A) 60 gtt/min
B) 75 gtt/min
C) 125 gtt/min
D) 1.25 gtt/min
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🎯 Bonus Practice
1. Infuse 500 mL over 6 hours with a 15 gtt/mL set. Drip rate?
A) 14 gtt/min
B) 21 gtt/min
C) 28 gtt/min
D) 83 gtt/min
2. Order: 1,500 mL over 12 hours. What is mL/hr?
A) 100 mL/hr
B) 125 mL/hr
C) 150 mL/hr
D) 180 mL/hr
3. An IV runs at 80 mL/hr with a 10 gtt/mL set. What is the drip rate?
A) 8 gtt/min
B) 13 gtt/min
C) 80 gtt/min
D) 800 gtt/min
4. How long will 750 mL last at 150 mL/hr?
A) 3 hours
B) 4 hours
C) 5 hours
D) 7.5 hours
5. Order: 100 mL over 30 minutes with a 20 gtt/mL set. Drip rate?