IV Drip Rate Calculator: gtt/min, mL/hr, and Infusion Time
Enter the volume, time, and drop factor to get the drip rate in drops per minute, with the formula and each step shown. The calculator also gives pump rates in mL/hr, how long an infusion will run, and the mL/hr rate for a weight-based mcg/kg/min order.
- Time: 8 h = 480 minutes
- 1000 mL × 15 gtt/mL = 15,000 gtt
- 15,000 gtt ÷ 480 min = 31.25, rounded to 31 gtt/min
How to calculate a drip rate
For gravity tubing, drops per minute = volume (mL) × drop factor (gtt/mL) ÷ time (minutes). The drop factor is printed on the tubing package: macrodrip sets deliver 10, 15, or 20 drops per mL and microdrip sets deliver 60. Drops cannot be counted in fractions, so the result is rounded to a whole number.
For an infusion pump, mL/hr = volume ÷ time in hours. Infusion time is the reverse: volume ÷ rate. For a weight-based order in mcg/kg/min, multiply the dose by the weight in kilograms and by 60 minutes, then divide by the bag concentration in mcg/mL.
A calculator result is a check on the hand calculation. The order, the pump library, and facility policy decide what is set, and a pharmacist can confirm an unusual rate.
Practice problems
Work each problem by hand, then open the answer to check it.
- Infuse 1,000 mL over 8 hours with a drop factor of 15 gtt/mL. How many gtt/min?
Show answer
31 gtt/min. 8 h = 480 min. 1,000 × 15 ÷ 480 = 31.25, rounded to 31 gtt/min.
- Infuse 500 mL over 4 hours on a pump. What is the rate in mL/hr?
Show answer
125 mL/hr. 500 mL ÷ 4 h = 125 mL/hr.
- Infuse 250 mL over 30 minutes with microdrip tubing (60 gtt/mL). How many gtt/min?
Show answer
500 gtt/min. 250 × 60 ÷ 30 = 500 gtt/min.
- A 1,000 mL bag runs at 125 mL/hr. How long will it take?
Show answer
8 hours. 1,000 ÷ 125 = 8 hours.
- The order is 5 mcg/kg/min for a 70 kg patient. The bag holds 400 mg in 250 mL. What is the rate in mL/hr?
Show answer
13.1 mL/hr. Concentration: 400 mg = 400,000 mcg ÷ 250 mL = 1,600 mcg/mL. 5 × 70 × 60 = 21,000 mcg/hr. 21,000 ÷ 1,600 = 13.1 mL/hr.
Questions
- What is the formula for drops per minute?
- Volume in mL multiplied by the drop factor in gtt/mL, divided by the time in minutes. 1,000 mL over 8 hours at 15 gtt/mL is 1,000 × 15 ÷ 480 = 31 gtt/min.
- What is a drop factor?
- The number of drops that make 1 mL with a given IV tubing set, printed on the package. Macrodrip sets are 10, 15, or 20 gtt/mL; microdrip sets are 60 gtt/mL.
- How do you convert mL/hr to gtt/min?
- Multiply mL/hr by the drop factor and divide by 60. With microdrip tubing (60 gtt/mL), gtt/min equals mL/hr.