Quick Answer
1 mL is about 20 drops from a standard eye dropper. However, the exact number of drops per mL depends on the dropper and liquid being measured. On average, 1 mL equals:
- 20 drops from an eye dropper
- 15 drops from a medicine dropper
- 25 drops from an essential oil dropper
When precision matters, it’s better to use a graduated cylinder or syringe instead of a dropper. But for rough measurements, a dropper can be a quick and convenient way to estimate 1 mL.
What is a Dropper?
A dropper, also called an eye dropper, is a simple device used to transfer small volumes of liquid. It consists of a squeezable bulb attached to a thin glass tube with a narrow opening. By squeezing and releasing the bulb, suction is created to draw liquid into the tube. Droppers are commonly used for:
- Administering medicine, vitamins, or eye drops
- Transferring essential oils, food coloring, or reagents
- Measuring approximate liquid volumes
Droppers allow the controlled release of liquids, one drop at a time. The size of each drop depends on the liquid’s density, surface tension, and the dropper’s orifice size. Water forms drops around 0.05 to 0.1 mL each. Thicker liquids like oils produce smaller drops.
How Many Drops in 1 mL?
The number of drops in 1 mL can vary substantially based on:
- Dropper type – medicine, eye, essential oil, etc.
- Dropper orifice/tip size – diameter and shape
- Liquid being measured – viscosity and surface tension
- Method of dropping – angle, squeeze force, height above surface
- Environmental factors – temperature, humidity, air pressure
With all these variables, measuring by drops can only provide a rough estimate of volume. However, we can make some generalizations:
| Dropper Type | Drops per mL |
|---|---|
| Eye dropper | 20 drops |
| Medicine dropper | 15 drops |
| Essential oil dropper | 25 drops |
These values represent averages, but the actual number can differ by ±5 drops depending on the factors listed above. For example, an eye dropper may produce anywhere from 15-25 drops per mL.
Eye Droppers
Eye droppers have a relatively large orifice of approximately 1 mm diameter. The large opening allows watery liquids like saline solutions and food coloring to easily form drops around 0.05 mL. So on average, 1 mL contains 20 drops from an eye dropper.
However, eye droppers are not very precise. Orifice size and drop volume can vary between different eye droppers. The number of drops per mL also depends on user technique.
Medicine Droppers
Medicine droppers have a smaller orifice, around 0.7 mm across. This allows better control over drop size for administering medications. Medicine droppers average around 15 drops per mL. But again, there is a wide range of 10-20 drops per mL depending on the exact dropper and liquid.
Essential Oil Droppers
Essential oil droppers produce the smallest drops. The tip opening is only around 0.5 mm diameter. This allows better precision when measuring expensive essential oils. The typical range is 20-30 drops per mL, averaging around 25 drops.
Variables that Affect Drops per mL
Many variables beyond the dropper type can alter the number of drops per milliliter. These include:
1. Liquid Viscosity
The viscosity or thickness of a liquid affects how readily it drips from the dropper. Thin liquids like water and alcohol form larger drops, while thick liquids like oils produce smaller drops:
- Water: ~0.05 mL per drop
- Alcohol: ~0.04 mL per drop
- Oil: ~0.02 mL per drop
So the more viscous the liquid, the more drops are required to reach 1 mL.
2. Liquid Surface Tension
Surface tension describes how well a liquid holds itself together. Liquids with higher surface tension form droplets more readily. Detergents and surfactants that lower surface tension allow liquids to sheet off surfaces more easily, producing larger drops.
3. Dropper Tip Size
The diameter of the dropper tip opening directly controls drop size. Larger openings form bigger drops. A dropper with a bigger tip will produce fewer drops per mL.
4. Method of Dropping
How the drops are formed can also affect their size and volume. Variables include:
- Squeeze force – Harder squeezes emit larger drops
- Drop height – Holding the dropper higher produces larger drops
- Angle of tilt – Keeping the dropper more vertical makes larger drops
Standard technique is to hold the dropper vertically about an inch above the surface and gently squeeze just enough to release a drop.
5. Temperature
At higher temperatures, liquids become less viscous so they flow more easily and form larger drops. Temperature also impacts surface tension. So the number of drops per milliliter decreases with increasing temperature.
6. Environmental Factors
Barometric pressure, humidity, and vapor saturation can also have subtle effects on droplet formation and evaporation. Drops may be slightly larger at higher humidity or pressure.
How to Measure 1 mL Using a Dropper
To measure 1 mL using a dropper:
- Select a clean glass medicine, eye, or essential oil dropper.
- Draw liquid into the dropper above the 1 mL line.
- Hold the filled dropper vertically about 1 inch over the container.
- Slowly squeeze the dropper, allowing drops to fall back into the container and count the drops as you go.
- Stop when you reach the expected number of drops for 1 mL based on the type of dropper and liquid.
For water and an eye dropper, count out 20 drops. For a medicine dropper dispensing oil, count 15 drops.
This video demonstrates drawing up 1 mL into a dropper and dispensing it out drop-wise:
Volume Variability Using Droppers
While droppers allow rough volume measurements, there can be substantial variability. Some sources of error include:
- Inconsistent drop size
- Miscounting drops
- Variation in dropper orifice size
- Changes in technique and environmental factors
- Evaporation loss between collecting and dispensing drops
One study found the accuracy of eye droppers to be just ±23% when measuring distilled water.* That means 1 mL could be off by 0.2 to 0.3 mL in either direction.
For any critical application requiring accuracy and precision, pipettes or volumetric labware should be used rather than droppers. However, droppers are suitable for rough measurements and estimates.
Alternatives for Measuring 1 mL
For accurate and precise 1 mL measurements, consider the following alternatives:
Graduated Cylinder
Graduated cylinders allow measurement to within ±2% accuracy when carefully read at eye level. 1 mL graduated cylinders are ideal for measuring small volumes.
Volumetric Flask
Class A volumetric flasks are designed for highly accurate volume measurements, to within ±0.1% when carefully filled to the calibration line. 1 mL volumetric flasks are available.
Micropipette
Micropipettes are adjustable air displacement pipettes capable of precisely measuring and dispensing volumes as small as 0.1 μL. Digital micropipettes provide the highest accuracy.
Syringe
Small syringes with volume markings can precisely measure down to 0.1 mL increments. However, the volume accuracy depends on the syringe quality.
Analytical Balance
An analytical balance capable of 0.1 mg resolution can accurately measure 1 mL volumes by weight, assuming a liquid density of 1 g/mL.
When to Use a Dropper for 1 mL
Droppers can be useful for measuring approximate 1 mL volumes when:
- Precision better than ±25% is not required
- Small amounts of costly liquid need to be conserved
- Volumes need to be transferred or dispensed drop-wise
- Proper measuring tools are unavailable
Common examples include:
- Estimating amounts of food coloring, extracts, or reagents
- Dispensing oils, fragrances, or flavorings
- Drawing up and administering medicine or supplements
- Roughly measuring for cleaning solutions, cosmetics, or DIY projects
As long as the user accounts for the variability in drop size, droppers can provide a quick and simple way to estimate 1 mL liquid volumes.
Conclusion
In summary, the number of drops per milliliter depends primarily on the type of dropper used and the liquid being measured. On average:
- 1 mL equals 20 drops from an eye dropper
- 1 mL equals 15 drops from a medicine dropper
- 1 mL equals 25 drops from an essential oil dropper
Many other factors like viscosity, tip size, technique, and temperature also influence drop size. While droppers can only provide a rough volume estimate, they serve as a convenient tool when precision is not critical. For accuracy, gravitational or volumetric labware should be used instead. But for quick everyday measurements, a simple dropper can often suffice.
