What it is
The IV flow rate (drip rate) converts a prescribed fluid volume and an infusion time into a deliverable rate — either an hourly volume (mL/hr) for a pump, or drops per minute (gtt/min) when you are counting drops on a gravity set. It is bedside arithmetic, but getting it wrong on a small child is a dosing error, so it is worth a deterministic tool rather than mental maths under pressure.
Formula
$$ Rate,(mL/hr) = \frac{volume,(mL)}{time,(hr)} $$
$$ Drip\ rate,(gtt/min) = \frac{volume,(mL) \times drop\ factor,(gtt/mL)}{time,(min)} $$
The drop factor is a property of the giving set: macrodrip sets deliver 10, 15, or 20 gtt/mL; a microdrip set delivers 60 gtt/mL and is used for small, precise pediatric volumes. The calculator takes volume, time in hours, and the drop factor, and returns both the mL/hr rate and the gtt/min drip rate.
When to use it
- Setting up a gravity infusion when no volumetric pump is available.
- Cross-checking a pump’s programmed rate against the prescription.
- Teaching/verifying drop counting in transport or resource-limited settings.
- Reconciling a documented mL/hr order with the physical giving set actually hanging at the bedside before a handover.
Worked example
Order: 500 mL over 4 hours through a macrodrip 15 gtt/mL set.
$$ Rate = \frac{500}{4} = 125\ mL/hr $$
$$ Drip\ rate = \frac{500 \times 15}{4 \times 60} = \frac{7500}{240} \approx 31\ gtt/min $$
So you run roughly 31 drops per minute, equivalent to 125 mL/hr. Count drops against a watch for a full 15–30 seconds and adjust the roller clamp.
Pitfalls
- Use a pump for children. Gravity drip counting is a fallback. For pediatric and especially neonatal volumes, a volumetric infusion pump set in mL/hr is far safer — gravity rates drift with bag height, patient position, and venous pressure.
- Wrong drop factor. Plugging a macrodrip figure into a microdrip set (or vice versa) is off by up to 6×. Confirm the gtt/mL printed on the set.
- Time units. The drip-rate formula needs minutes; the mL/hr formula needs hours. Mixing them is a classic slip.
- Rounding. Drops are discrete — round the gtt/min to a whole number, but don’t let rounding hide a clinically meaningful rate change.
- No free-flow safeguard. Gravity sets have no occlusion/air alarms; reassess frequently.
Run it: [IV Flow Rate (Drip Rate)](/calculator/iv-flow-rate)
Decision support for qualified clinicians only — verify against current primary guidelines and your clinical judgement.