How to calculate IV flow rates:

Intravenous fluid must be given at a specific rate, neither too fast nor too slow. The specific rate may be measured as ml/hour, L/hour or drops/min. To control or adjust the flow rate only drops per minute are used.

The burette contains a needle or plastic dropper which gives the number of drops per ml (the drop factor). A number of different drop factors are available (determined by the length and diameter of the needle).

Common drop factors are:
10 drops/ml (blood set), 15 drops / ml (regular set), 60 drops / ml (microdrop).

To measure the rate we must know:
(a) the number of drops
(b) time in minutes.

The formula for working out flow rates is:

volume (ml) X drop factor (gtts / ml)
---------------------------------------------
time (min)

= gtts / min
(flow rate)

Example:

1500 ml IV Saline is ordered over 12 hours. Using a drop factor of 15 drops / ml, how many drops per minute need to be delivered?

1500 (ml) X 15 (gttss / ml)
---------------------------------------------------
12 x 60 (gives us total minutes)

= 31 gtts / minute