Drip rate formula
The drip rate in drops per minute is the volume multiplied by the drop factor of the administration set, divided by the infusion time in minutes.
An infusion pump takes the flow rate in mL/hr instead, which needs no drop factor.
To convert a known mL/hr into drops per minute, multiply by the drop factor and divide by 60. For a gravity set counted with a watch, seconds per drop is 60 divided by the drops per minute.
Each drop factor reduces to a single division of mL/hr: divide by 6 on a 10 gtt/mL set, by 4 on a 15 gtt/mL set and by 3 on a 20 gtt/mL set. On a 60 gtt/mL microdrip set the factor and the 60 cancel, so drops per minute equals mL/hr.
Drop factor chart
The drop factor is the number of drops the administration set delivers per mL. It is set by the size of the drip chamber orifice and printed on the set's package. Macrodrip sets deliver 10, 15 or 20 gtt/mL depending on the manufacturer. Microdrip sets deliver 60 gtt/mL.
Drops per minute at 100 mL/hr shows how far apart the sets are at the same flow rate.
| Drop factor | Set type | Volume per drop | gtt/min at 100 mL/hr |
|---|---|---|---|
| 10 gtt/mL | Macrodrip | 0.1 mL | 16.7 |
| 15 gtt/mL | Macrodrip | 0.067 mL | 25 |
| 20 gtt/mL | Macrodrip | 0.05 mL | 33.3 |
| 60 gtt/mL | Microdrip | 0.017 mL | 100 |
A microdrip set gives more drops per mL, so a low hourly rate still produces a drip fast enough to count. At 10 mL/hr a 60 gtt/mL set drips once every 6 seconds, where a 10 gtt/mL set drips once every 36 seconds.
mL/hr to gtt/min chart
Drops per minute for common flow rates at each drop factor, rounded to one decimal place. Round to the nearest whole drop when setting a gravity drip. Below a few drops per minute that rounding moves the rate by 20 percent or more, so set the drip by seconds per drop or use a microdrip set.
| Flow rate | 10 gtt/mL | 15 gtt/mL | 20 gtt/mL | 60 gtt/mL |
|---|---|---|---|---|
| 5 mL/hr | 0.8 | 1.3 | 1.7 | 5 |
| 10 mL/hr | 1.7 | 2.5 | 3.3 | 10 |
| 15 mL/hr | 2.5 | 3.8 | 5 | 15 |
| 20 mL/hr | 3.3 | 5 | 6.7 | 20 |
| 25 mL/hr | 4.2 | 6.3 | 8.3 | 25 |
| 30 mL/hr | 5 | 7.5 | 10 | 30 |
| 40 mL/hr | 6.7 | 10 | 13.3 | 40 |
| 50 mL/hr | 8.3 | 12.5 | 16.7 | 50 |
| 60 mL/hr | 10 | 15 | 20 | 60 |
| 75 mL/hr | 12.5 | 18.8 | 25 | 75 |
| 80 mL/hr | 13.3 | 20 | 26.7 | 80 |
| 100 mL/hr | 16.7 | 25 | 33.3 | 100 |
| 125 mL/hr | 20.8 | 31.3 | 41.7 | 125 |
| 150 mL/hr | 25 | 37.5 | 50 | 150 |
| 200 mL/hr | 33.3 | 50 | 66.7 | 200 |
| 250 mL/hr | 41.7 | 62.5 | 83.3 | 250 |
Weight-based fluid rates
Veterinary fluid plans are usually written per kilogram, as mL/kg/hr or mL/kg/day, because patient size ranges from tens of grams to several hundred kilograms. Multiply by body weight in kilograms to get the hourly rate.
Convert pounds to kilograms by dividing by 2.2046. The calculator's weight field switches between kg and lb and converts for you.
A deficit volume for rehydration, as set out in the 2024 AAHA fluid therapy guidelines, is the body weight in kilograms multiplied by the estimated percent dehydration as a decimal, which gives liters. A 10 kg patient estimated at 5 percent dehydrated has a deficit of 0.5 L, or 500 mL. The period over which the deficit is replaced is a clinical decision, and the result goes into the volume and time fields above.
Worked examples
1,000 mL over 8 hours on a 15 gtt/mL set
1,000 mL × 15 gtt/mL = 15,000 drops. 8 hours is 480 minutes, and 15,000 ÷ 480 = 31.25, so the drip rate is 31 gtt/min. The flow rate is 1,000 ÷ 8 = 125 mL/hr. At 31.25 gtt/min there is one drop every 1.9 seconds, or about 5 drops in 10 seconds.
30 mL/hr on a 60 gtt/mL microdrip set
30 × 60 ÷ 60 = 30 gtt/min, one drop every 2 seconds. On a microdrip set gtt/min always equals mL/hr.
1,200 mL a day on a 20 gtt/mL set
1,200 ÷ 24 = 50 mL/hr. 50 × 20 ÷ 60 = 16.7, so the drip rate is 17 gtt/min, one drop every 3.6 seconds.
Rehydrating a 30 kg dog on a 15 gtt/mL set
At an estimated 6 percent dehydration the deficit is 30 × 0.06 = 1.8 L, or 1,800 mL. Replaced over 12 hours, that is 1,800 ÷ 12 = 150 mL/hr, and 150 ÷ 4 = 37.5 gtt/min, about 6 drops every 10 seconds. Maintenance and ongoing losses are added on top of the deficit rate.
10 mL/hr on a microdrip set
On a 60 gtt/mL set, 10 mL/hr is 10 gtt/min, one drop every 6 seconds. The same rate on a 15 gtt/mL set is 2.5 gtt/min, one drop every 24 seconds.
250 mL at 50 mL/hr
250 ÷ 50 = 5, so the bag runs for 5 hours. Run time is the volume divided by the flow rate in mL/hr.
How to count and set a gravity drip
- Read the drop factor off the set's package before calculating. Sets from different manufacturers differ. Between macrodrip sets the wrong factor halves or doubles the rate, and mistaking a microdrip set for a macrodrip set changes it three- to sixfold.
- Work out the target in drops per 10 seconds, which is gtt/min divided by 6. At slow rates, timing the gap between drops in seconds is easier than counting.
- Open the roller clamp and count against a watch for 10 seconds and compare with the target. Count for a full minute to confirm once the rate looks right.
- Mark the bag with the expected level at each hour, so the running volume can be checked against the plan at every treatment.
- Recount after the patient moves. A gravity drip changes with bag height and catheter position, so a rate set with the patient lying down can slow or stop when it sits up or bends a limb.
A gravity set gives an approximate rate. Where the volume has to be precise, such as small patients or fluid-sensitive cases, an infusion pump or syringe pump set in mL/hr is the usual choice.
Drip rate questions
How do you calculate IV drip rate?
Multiply the volume in mL by the drop factor of the administration set in gtt/mL, then divide by the infusion time in minutes. 1,000 mL over 8 hours on a 15 gtt/mL set is 1,000 times 15 divided by 480, which is 31.25, rounded to 31 gtt/min.
How do you convert mL/hr to gtt/min?
Multiply the rate in mL/hr by the drop factor and divide by 60. 100 mL/hr on a 20 gtt/mL set is 100 times 20 divided by 60, which is 33.3 gtt/min. On a 60 gtt/mL microdrip set, gtt/min is the same number as mL/hr.
What does gtt mean?
gtt is the abbreviation for drops, from the Latin guttae. gtt/min is drops per minute and gtt/mL is the drop factor of an administration set.
How many drops are in 1 mL?
It depends on the administration set. A macrodrip set delivers 10, 15 or 20 drops per mL depending on the manufacturer, and a microdrip set delivers 60. The figure is printed on the set's package as the drop factor.
What is the difference between macrodrip and microdrip?
A macrodrip set delivers 10 to 20 drops per mL and suits higher flow rates. A microdrip set delivers 60 drops per mL, so each drop is smaller and a low hourly rate still produces a countable drip.
How do you calculate a fluid rate for a dog or cat?
Multiply the patient's weight in kilograms by the ordered rate in mL/kg/hr to get mL/hr, then convert to drops per minute if a gravity set is being used. A rate written per day in mL/kg/day is divided by 24 first. The rate itself comes from the patient's fluid plan.
How do you calculate the rate for an IV infusion pump?
Divide the volume to be given by the time in hours. 500 mL over 4 hours is 125 mL/hr. A pump takes mL/hr directly, so no drop factor is needed. For a weight-based order, multiply the weight in kilograms by the rate in mL/kg/hr.
How do you calculate fluid volume per day?
Multiply the rate in mL/hr by 24. 50 mL/hr is 1,200 mL a day. For a plan written in mL/kg/day, multiply the rate by the weight in kilograms.
What is the 4-2-1 rule for fluids?
The 4-2-1 rule is the hourly form of the Holliday-Segar method for maintenance fluids in human pediatrics, which sets 100, 50 and 20 mL/kg/day: 4 mL/kg/hr for the first 10 kg of body weight, 2 mL/kg/hr for the next 10 kg and 1 mL/kg/hr for each kg above 20. It was derived from the energy expenditure of children. Maintenance rates for dogs and cats come from veterinary guidance such as the 2024 AAHA Fluid Therapy Guidelines for Dogs and Cats.
How do you calculate how long an IV bag will last?
Divide the volume left in the bag by the flow rate in mL/hr. 500 mL at 125 mL/hr lasts 4 hours.
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About this calculator
The calculator does arithmetic on the numbers entered. It does not choose a fluid, a rate or a volume, and the result should be checked against the written order and the drop factor on the set before use.
Found an error? Tell us at [email protected] and we will correct it.
Last updated 30 September 2026.