IV Drip Rate Calculator — Drops Per Minute (gtt/min)

A manual gravity IV drip has no pump — the fluid falls through the drip chamber and you set the flow by counting drops per minute. The number of drops that make up one millilitre is fixed by the giving set and is called the drop factor (gtt/mL). Macrodrip sets are calibrated at 10, 15 or 20 gtt/mL; the microdrip (paediatric) set is 60 gtt/mL. This value is printed on the packaging and is the single most important input.

The drip-rate formula from Deborah Gray Morris' Calculate with Confidence, the standard nursing dosage-calculation text, is:

gtt/min = (volume in mL × drop factor in gtt/mL) ÷ time in minutes

First the time is normalised to minutes — hours are multiplied by 60. Then volume times drop factor gives the total number of drops in the bag, and dividing by the number of minutes spreads them evenly across the infusion. The result is rounded to the nearest whole drop for display, because you count whole drops in the chamber and cannot set a fraction of one.

The same order can also be described as a flow rate in mL/hr, which is what an infusion pump uses:

flow rate mL/hr = volume in mL ÷ time in hours

You can get drops per minute directly from a known pump rate with gtt/min = (mL/hr × drop factor) ÷ 60. This is algebraically identical to the first formula, so the tool computes both paths and shows they agree — a built-in check against arithmetic slips. In infusion-time mode the tool works backwards from a pump rate instead, using time in hours = volume ÷ flow rate, and renders the answer as whole hours plus remainder minutes.

Finally, two bedside counting aids are derived from the drip rate: seconds per drop (60 ÷ gtt/min) and drops per 15 seconds (gtt/min ÷ 4), so you can time the chamber against a watch. One well-known shortcut falls out of the maths: with a 60 gtt/mL microdrip set, drops per minute always equal the mL/hr rate, because dividing by 60 (the drop factor) and then the 60 minutes in an hour cancels out.

• Gray Morris, D. — Calculate with Confidence (Elsevier): drip-rate, flow-rate and infusion-time formulas
• B. Braun — IV administration sets, instructions for use (drop-factor calibration)
• RegisteredNurseRN — IV flow-rate calculations (NCLEX-standard cross-check)

The formulas and drop-factor values on this page were last cross-checked against these sources on 2026-07-17. This tool is an educational aid for a single ordered gravity infusion. It does not validate the prescription, cover weight-based drug dosing, and is not a substitute for an infusion pump or a qualified clinician's judgement.