What this calculator does
An IV giving set delivers fluid in individual drops, and different sets are calibrated to different drop factors: how many drops make up one millilitre. To infuse a prescribed volume over a prescribed time, the drip rate in drops per minute depends on both of those things together with the drop factor of the specific giving set in use.
This calculator takes the volume to infuse, the total time, and the giving set's drop factor, and returns the drops-per-minute rate along with the equivalent flow rate in millilitres per hour. It performs the arithmetic only; the volume and time to infuse are prescribed by a clinician, and this does not calculate or suggest either of those.
The formula
Multiply the volume to infuse (in mL) by the drop factor (drops per mL), then divide by the total infusion time in minutes.
| Term | Meaning |
|---|---|
| Drop factor | How many drops of fluid make up 1 mL with a specific giving set, printed on the set's packaging. Standard sets are commonly 15 or 20 drops/mL; blood sets around 10; micro/paediatric sets 60. |
| Drip rate | How many drops per minute the infusion should run at to deliver the prescribed volume over the prescribed time. |
The inputs explained
| Field | What to enter |
|---|---|
| Volume to infuse (mL) | The total volume to be infused, in millilitres, as prescribed. |
| Time (hours) | The whole hours of the prescribed infusion time. |
| Time (extra minutes) | Any extra minutes beyond the whole hours, if the prescribed time isn't a round number of hours. |
| Drop factor (giving set) | The drop factor printed on the specific giving set being used. Using the wrong set's drop factor gives the wrong drip rate. |
When to use it
Setting up a gravity-fed infusion
Where a pump isn't used and the rate is controlled by counting drops, this converts a prescribed volume and time into the drops-per-minute rate to count against a watch.
Converting between drop factor sets
Swapping the drop factor to match a different giving set on hand shows how the same prescribed volume and time translates to a different drip rate.
Cross-checking a pump's mL/hr setting
The mL/hr figure this returns can be checked against what an infusion pump would be set to for the same prescribed volume and time.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How does drip rate change with the giving set, for 1000 mL over 8 hours?
The same prescribed volume and time, run through each common giving-set drop factor.
| Drop factor | Drip rate |
|---|---|
| 10 drops/mL | 20.8 drops/min |
| 15 drops/mL | 31.3 drops/min |
| 20 drops/mL | 41.7 drops/min |
| 60 drops/mL | 125.0 drops/min |
Questions
What if I don't know the giving set's drop factor?
It's printed on the giving set's packaging. Using the wrong drop factor produces an incorrect drip rate, so it should always be confirmed from the set actually in use rather than assumed.
Does this calculate the prescribed volume or time for me?
No. The volume to infuse and the total time are clinical decisions prescribed separately; this only converts those two prescribed figures, together with the giving set's drop factor, into a drip rate.
Why does a micro drip set need a much faster drip rate?
A micro (60 drops/mL) set delivers much smaller drops than a standard (15–20 drops/mL) set, so many more of them are needed to deliver the same volume in the same time.
Is mL/hr or drops/min more useful?
An infusion pump is set in mL/hr directly. A manual gravity-fed infusion is counted in drops/min against a watch, since there's no pump display. This calculator gives both.
For a general concentration or dilution calculation, see the dilution ratio calculator.