IV drip rate calculator
Enter the volume to infuse, the time it should run over and the drop factor printed on the giving set. You get the drip rate in drops per minute, the pump rate in mL/h and the number of drops to count in 15 seconds. It is a calculation aid; always follow the prescription and your local protocol.
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How to use it
- Enter the volume in millilitres.
- Enter the time in hours and minutes, for example 2 h 30 min.
- Choose the drop factor printed on the giving set.
- Set the roller clamp so the chamber drips at the rate shown; counting for 15 seconds and comparing with the last line is quicker than counting a full minute.
- Drops per minute = volume (mL) × drop factor (gtt/mL) ÷ time (min)
- Pump rate (mL/h) = volume (mL) ÷ time (h)
- Drops in 15 seconds = drops per minute ÷ 4
Worked example
1000 mL of saline over 8 hours with a 20 drop/mL set: 8 h = 480 min, so 1000 × 20 ÷ 480 = 41.7 gtt/min, and 1000 ÷ 8 = 125 mL/h. In 15 seconds you should count 41.7 ÷ 4 = 10.4, about 10 drops.
With a 15 drop/mL set, 500 mL over 4 hours is 500 × 15 ÷ 240 = 31.25 drops a minute, shown as 31.3 gtt/min.
Tips and common mistakes
- Drops cannot be split: round to the nearest whole drop when setting the clamp.
- Use the drop factor of the set in your hand; using 20 when the set is 15 makes the infusion run a third faster than planned.
- Gravity rates drift as the bag empties, the patient moves or the cannula kinks. Check the rate regularly.
- This is a calculation aid. Always check against the prescription and your local policy.
Frequently asked questions
What is the formula for drops per minute?
Drops per minute = volume in mL × drop factor in drops per mL ÷ time in minutes. For 1000 mL over 8 hours with a 20 drop set: 1000 × 20 ÷ 480 = 41.7, so about 42 drops a minute.
What is a drop factor?
The number of drops that make 1 mL with a given giving set. It is printed on the packet. Macrodrip sets give 10, 15 or 20 drops/mL depending on the maker, and microdrip sets give 60 drops/mL. Always read the packet rather than assuming.
Why is the pump rate the same for every drop factor?
A pump is set in mL per hour, which depends only on volume and time: 1000 mL over 8 hours is 125 mL/h with any giving set. The drop factor only matters when you count drops for a gravity infusion.
Why does a microdrip set give drops per minute equal to mL/h?
With 60 drops per mL, drops per minute = mL × 60 ÷ minutes, which is the same number as mL per hour. 100 mL/h is 100 drops a minute.