Drops to mL Conversion Calculator NZ
This calculator converts between drops (gtt) and millilitres in either direction, using whatever drop factor matches your dropper, medicine bottle, or IV giving set. A drop is not a fixed unit of volume, since its size depends on the liquid's viscosity and the width of the dropper tip, so you first choose a drop factor: the standard 20 drops per mL used for most medicine and eye droppers, an IV macrodrip rate of 15 or 10 gtt/mL, a microdrip or paediatric rate of 60 gtt/mL, or your own custom figure if the packaging states something different. Next you pick a direction, either drops to millilitres or millilitres to drops, and enter the number of drops or the volume you are converting. The calculator returns the equivalent drops, millilitres, and drop factor used, plus a breakdown of your conversion and a table of common conversions at that factor, from 1 through to 100 drops. Use it to check a dose, work out how much liquid a set number of drops makes up, or convert a volume into drops for a dropper or IV set. Because drop size varies between liquids and equipment, always confirm the exact drop factor printed on the packaging or giving set label rather than assuming one universal rate, and for medicine dosed in drops, follow your pharmacist's or doctor's instructions rather than a generic conversion.
1. Drop Factor
2. Convert
Common Conversions at This Drop Factor
| Drops | Millilitres | Drops | Millilitres |
|---|
Your Conversion
Reference Drop Factors
How Drops to mL Conversion Works
A drop is not a fixed unit of volume. Unlike millilitres, teaspoons, or litres, the size of a drop depends on the liquid's viscosity and surface tension and on the size of the opening it falls from. To convert drops to millilitres, you need a drop factor: the number of drops that make up one millilitre for that specific dropper or liquid. The formula is straightforward once you know the drop factor.
The Formula
Millilitres = Number of drops ÷ Drop factor (drops per mL). Conversely, Drops = Millilitres × Drop factor. For example, at the standard rate of 20 drops per mL, 20 drops equal 1 mL, and 100 drops equal 5 mL.
Common Drop Factors
| Use | Drop Factor | 1 mL equals |
|---|---|---|
| Standard medicine or eye dropper | 20 gtt/mL | 20 drops |
| IV macrodrip set (common) | 15 gtt/mL | 15 drops |
| IV macrodrip set (wide bore) | 10 gtt/mL | 10 drops |
| IV microdrip / paediatric set | 60 gtt/mL | 60 drops |
The 20 drops per mL figure is the most widely used general reference for water-based liquids like saline nasal spray, eye drops, and many liquid medicines. IV giving sets are labelled with their own drop factor by the manufacturer, and this is what nurses use to calculate drip rates. Always check the packaging or prescribing information rather than assuming a single universal rate, since thicker liquids form larger drops and therefore fewer drops per millilitre.
Why This Matters
Getting the drop factor wrong can lead to dosing errors, particularly with medicines where drops are used to measure small, precise amounts (such as paediatric medicine, eye drops, or concentrated liquid supplements). If a medicine label specifies a dose in drops rather than mL, use the drop factor stated on that specific product's packaging or accompanying leaflet, not a generic assumption. This calculator is a reference tool for general conversion and does not replace instructions from a pharmacist, doctor, or product label.
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Sources: Standard pharmacy drop factor conventions (20 gtt/mL for medicine droppers). IV administration set drop factors as commonly published by New Zealand district health board medicines information services and manufacturer packaging (10, 15, 20, and 60 gtt/mL sets).
This calculator provides a general reference conversion only. Actual drop size varies by liquid and dropper. For any medicine dosed in drops, always follow the drop factor and instructions on the product packaging or from your pharmacist or doctor, not a generic conversion.