BioDeviceHub

Drip Rate Calculator

Calculate the drip rate in drops per minute for a gravity infusion from the volume, time and the drop factor of the giving set, as educational arithmetic.

Formula

dropsmin=V (mL)×drop factor (drops/mL)t (min)\dfrac{\text{drops}}{\mathrm{min}} = \dfrac{V\,(\mathrm{mL})\times \text{drop factor}\,(\mathrm{drops/mL})}{t\,(\mathrm{min})}
seconds per drop=60drops per minute\text{seconds per drop} = \dfrac{60}{\text{drops per minute}}
drop factor\text{drop factor}
drops per mL for the giving set: 10, 15 or 20 for macrodrip, 60 for microdrip
VV
volume to be infused, in mL
tt
time, in minutes

How it works

A gravity giving set delivers a fixed number of drops per millilitre, called its drop factor and printed on the packaging. The drip rate is the volume times the drop factor, divided by the time in minutes. A microdrip set, at 60 drops per millilitre, conveniently gives a rate in drops per minute equal to the rate in millilitres per hour.

Counting drops is an estimate. The rate drifts with the height of the bag, the position of the limb, the vein and the viscosity of the fluid, so it is rechecked at intervals, and a pump is used where accuracy matters.

Worked example

1,000 mL over 8 hours with a 20 drops/mL set.

  1. Time = 8 × 60 = 480 min.
  2. Rate = 1,000 × 20 / 480 = 41.7 drops/min.

About 42 drops per minute, or one drop every 1.4 seconds.

These are the values the calculator opens with, so you can check its output against this example.

Assumptions

  • The drop factor printed on the set in use.
  • A steady rate, which a gravity infusion does not maintain without attention.

Common mistakes

  • Using the drop factor of a different set.
  • Expecting a counted drip to stay constant without rechecking.
  • Calculating for one set and then using another.

Related tools

IV Flow Rate CalculatormL per hour from a volume and a time, or time and volume from a rateOpen calculatorWeight-Based Infusion Rate CalculatorPump rate from a dose per kg per minute and a concentrationOpen calculatorLaboratory Unit ConverterVolume, mass, length, time, pressure, electrical units and moreOpen calculator

Related equipment

Service documentation, failure modes and parts for the instruments this calculation is used with.