Ml and drops — drug calculations
Drip rate calculator: work out
drops per minute
A drip rate calculation is one of the most common steps in drug calculations. Here you get the formula, a clear explanation and a calculator you can use straight away, whether you are practising or just need to check a calculation quickly.
The drip rate formula
Drops per minute are worked out by combining volume, drop factor and time.
Time in minutes: 4 × 60 = 240 minutes
Drops/min = (500 × 20) ÷ 240 = about 41.7 drops per minute
Drip rate calculator
Fill in the values below to work out drops per minute straight away.
Work out drops per minute
The calculator is a study tool for practising drug calculations and should not be used as the basis for clinical dosing.
What is a drop factor?
The drop factor is the number of drops that make up 1 ml with a particular giving set, and it differs between types of equipment.
Macrodrip (20 drops/ml)
The most common drop factor for adults on standard infusions. Unless a question says otherwise, this is usually the one to use.
Microdrip (60 drops/ml)
Gives smaller drops and is used when more precise dosing is needed, for example for infusions in children or in intensive care. Always check the drop factor printed on the giving set you are using.
Need to dilute before the infusion? Work out the dilution here →
Need to calculate the amount of drug as well? See the dosage calculator →
Frequently asked questions about drip rate
How do you calculate drops per minute?+
Drops per minute = (volume in ml × drop factor) ÷ time in minutes. For example, 500 ml with a drop factor of 20 over 4 hours (240 minutes) gives (500 × 20) ÷ 240 = about 41.7 drops per minute.
What is a drop factor?+
The drop factor is the number of drops that make up 1 ml with a particular giving set. Common drop factors are 20 drops/ml (macrodrip, standard for adults) and 60 drops/ml (microdrip, often used for children or when precise dosing is needed).
What is the difference between macrodrip and microdrip?+
A macrodrip set has a drop factor of 20 (sometimes 15) drops/ml and is used for standard infusions. A microdrip set has a drop factor of 60 drops/ml and gives smaller drops, which is used when more precise dosing is needed.
How do you convert hours to minutes for a drip rate calculation?+
Multiply the number of hours by 60 to get the time in minutes. For example, 4 hours is 240 minutes, which you then use in the drip rate formula.
Why is drip rate part of drug calculations?+
Drip rate (ml and drops) is a standard topic in drug calculation courses, because getting the infusion rate right is essential for patient safety.
Practise drops and infusions in Dos
Drip rate is just one of the topics. Dos is a practice app for drug calculations, with practice tests of ten questions, a built-in calculator next to each question and statistics per topic.
