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MasterMath

IV Drip Rate Calculator

The drip rate of an infusion: how many drops per minute to set for a given volume over a given time, using the drop factor of whichever set you have.

Drops per minute

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Drops per minute—
Unrounded—
Equivalent to—
One drop every—
Set used—
Check—

How this was worked out

    Indicative result. The real rate of a gravity drip varies with bag height and patient position. It has to be checked periodically, and the prescription always sets the regimen.

    The formula

    drops/min = volume × set factor ÷ minutes

    Where it comes from

    Every infusion set delivers a fixed number of drops per millilitre, and that number is printed on the packet: macrodrip sets are usually 10, 15 or 20 drops per millilitre and microdrip sets 60. The arithmetic is a simple proportion: the millilitres to deliver become drops by multiplying by that factor, and are then spread across the minutes available.

    How to work it out by hand

    1. Check the packet for the set's drops per millilitre
    2. Multiply the volume in millilitres by that factor: those are the total drops
    3. Divide by the infusion time in minutes
    4. Round to whole drops and set the roller clamp by counting them

    What is worth knowing

    The 60-drop microdrip set has a property that saves arithmetic: since there are 60 minutes in an hour and 60 drops in a millilitre, drops per minute equal millilitres per hour exactly. A macrodrip set does not do that. And remember a gravity drip is not a pump: the rate changes with the height of the bag, the patient's position and the cannula itself, so it has to be rechecked.

    Frequently asked questions

    Where do I find the set's drop factor?

    On the infusion set packaging. It is printed as drops per millilitre, usually 10, 15, 20 or 60.

    Why is a microdrip set easier?

    Because at 60 drops per millilitre, drops per minute are exactly millilitres per hour. It saves the calculation.

    Do I round up or down?

    To the nearest whole number. Half a drop a minute is negligible against the drift of the drip itself.

    Does this work for infusion pumps?

    On a pump you programme millilitres per hour directly, which also appears here. Drops are for gravity drips.

    Why does the rate drift?

    Because it depends on pressure, which changes with bag height and arm position. That is why it needs rechecking.