What this calculator does
The drops per minute formula converts a prescribed IV infusion, a volume to be given over a set time, into a drip rate that can be counted at the bedside: drops per minute equals volume in millilitres times the drop factor in drops per millilitre, divided by the infusion time in minutes.
The drop factor is set by the specific giving set in use, not by the fluid or the patient, and it varies between equipment: common values include 10, 15 and 20 drops per millilitre for standard sets and 60 drops per millilitre for a microdrip set used with small or precise volumes. Getting the drop factor from the correct giving set, rather than assuming a default, is the step most likely to be missed.
The formula
Multiply the volume to be infused, in millilitres, by the drop factor of the giving set, in drops per millilitre. Divide that by the infusion time in minutes. The result is the number of drops per minute the infusion should run at.
| Term | Meaning |
|---|---|
| Drops per minute | The counted drip rate: (volume × drop factor) ÷ time in minutes. |
| Drop factor | How many drops make up one millilitre for a specific giving set, printed on its packaging. |
| Infusion time | The total time, in minutes, over which the volume is to be given. |
The inputs explained
| Field | What to enter |
|---|---|
| Volume to infuse (mL) | The total volume to be infused, in millilitres. |
| Drop factor (from the giving set) (drops/mL) | The drop factor of the giving set in use, in drops per millilitre. This varies by equipment, so check the set rather than assuming a value. |
| Infusion time (minutes) | The total infusion time, in minutes. |
When to use it
Working out a manual gravity infusion rate
Where an infusion pump is not in use, the drip rate has to be counted and set manually, and this is the standard calculation behind that count.
Checking a rate against a different giving set
Switching between a standard set and a microdrip set changes the drop factor, and therefore the drops-per-minute figure, for exactly the same volume and time.
Converting between a drip rate and an hourly flow rate
Some equipment or documentation specifies rate in mL per hour rather than drops per minute; this calculator shows both for the same infusion.
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 the drip rate changes with the drop factor
The same 1,000 mL infusion over 8 hours, at a range of drop factors.
| Drop factor | Drops per minute | Equivalent flow rate |
|---|---|---|
| 10 drops/mL | 20.8 drops/min | 125.0 mL/hr |
| 15 drops/mL | 31.3 drops/min | 125.0 mL/hr |
| 20 drops/mL | 41.7 drops/min | 125.0 mL/hr |
| 60 drops/mL | 125.0 drops/min | 125.0 mL/hr |
Questions
How to calculate drops per minute?
Multiply the volume to infuse, in millilitres, by the drop factor of the giving set, in drops per millilitre, then divide by the infusion time in minutes.
What drop factor should I use?
Use the value printed on the giving set actually connected, not a remembered default. Standard sets are commonly 10, 15 or 20 drops per millilitre, and microdrip sets are commonly 60 drops per millilitre.
Does this calculator tell me the correct infusion rate for a patient?
No. It only converts a volume and time that have already been prescribed into a drip rate. The volume, time and any medication content are set by the prescribing clinician’s order and facility protocol, not by this calculator.
Why does the same volume need such a different drops-per-minute figure with different drop factors?
A larger drop factor means each individual drop is smaller, so more of them are needed each minute to deliver the same total volume over the same time.
For a Glasgow Coma Scale assessment used alongside other bedside observations, see the GCS calculator.