When it comes to measuring liquid medication, it’s important to know the equivalent between drops and milliliters (mL). This allows you to accurately administer the correct dosage, especially when a medication is prescribed in mL but only available in drop form. So how many drops are in a mL? Let’s take a closer look.
The Short Answer
As a general rule of thumb:
- 20 drops = 1 mL
However, this can vary slightly depending on factors like the viscosity of the liquid, the size of the dropper, and individual drop size. But for the most part, 20 drops per mL is a good standard conversion to remember.
The Long Answer
While 20 drops per mL is a commonly used conversion, the exact number of drops per mL can range from 15-30 drops depending on the variables mentioned above. Here are some key points to understand about the drops-to-mL relationship:
Drop Size Varies
The size of an individual drop can range in size dramatically based on:
- The viscosity of the liquid – Viscous liquids like oils form larger drops than watery liquids.
- Dropper type – The material, orifice size, and design impacts drop size.
- Method – How quickly the drops are formed can change their size.
- Surface tension – This molecular property affects how readily drops form.
Due to these factors, the number of drops per mL can be as low as 15 or as high as 30 for different liquids and conditions. So while 20 drops/mL is a common benchmark, the actual conversion can vary.
Standard Conversions Used
In healthcare and pharmaceutical settings, standard conversions are often used for consistency and accuracy:
| Source | Drops per mL |
|---|---|
| World Health Organization (WHO) | 20 drops/mL |
| United States Pharmacopeia (USP) | 20 drops/mL |
| American Academy of Pediatrics (AAP) | 15 drops/mL |
As you can see, 15-20 drops/mL are commonly used standards, although WHO and USP recommend 20 drops/mL specifically when greater accuracy is needed.
Factors That Impact Drop Size
Let’s take a closer look at some of the key factors that can impact the size of an individual drop, and therefore the total drops per mL:
Viscosity
The thickness or viscosity of a liquid affects how readily drops form. Viscous liquids like syrups and oils tend to produce larger drops. Watery liquids like solutions produce smaller drops.
Dropper Tip
The size and shape of the droplets tip directly impacts drop size:
- Smaller tip = smaller drops
- Larger tip = larger drops
Additionally, the material the dropper is made from and Its design can affect fluid flow and drop formation.
Method
How quickly the drops are formed can also change their size. Large drops form when the liquid is squeezed forcefully. Smaller drops form when gently squeezed.
Surface Tension
Liquids have an intermolecular force called surface tension. Substances with higher surface tension produce larger drops. Lower surface tension allows smaller drops to form.
Temperature
Warmer temperatures can decrease viscosity and lower surface tension, allowing smaller drops to form.
How Drops are Measured
When establishing standard drop-to-mL conversions, drops are carefully measured under controlled conditions:
- Room temperature distilled water is often used.
- A consistent dropper type and squeezing force is applied.
- Measurements obtained by automated drop counters.
- An average of multiple tests is taken.
This helps minimize the impact of variables and provides an accurate standard conversion rate.
Key Considerations for Proper Dosing
When administering medications prescribed in mL using drop form, keep these tips in mind:
- Consult packaging for dropper specifications.
- Refer to medical standards like WHO for conversion rates.
- Use same dropper and technique each time.
- Count drops carefully and double check.
- Aim for lower end of range if concerned.
Doing this helps ensure proper dosage and safe administration.
Examples of Drops to mL Conversions
Here are some examples of how to convert commonly prescribed or OTC medication amounts from mL to drops:
Ibuprofen
Prescribed Dosage: 5 mL
Standard Conversion: 20 drops/mL
Calculation: 5 mL x 20 drops/mL = 100 drops
Cough Syrup (children)
Prescribed Dosage: 2.5 mL
AAP Standard: 15 drops/mL
Calculation: 2.5 mL x 15 drops/mL = 37.5 drops (round to 40 drops)
Infant Fever Reducer
Dosage: 0.8 mL
WHO Standard: 20 drops/mL
Calculation: 0.8 mL x 20 drops/mL = 16 drops
Tools to Help Measure in Drops
To facilitate counting drops, consider using:
- Oral syringes – Allow measuring dose then dispensing in drops.
- Automated drop counters – Count and dispense prescribed amount.
- Smart medicine bottles – Track doses and dispense proper amount.
Using tools like these can improve accuracy and make it easier to dose medications in drop form.
Proper Use of Droppers
To standardize drop size when dosing liquid medications:
- Hold dropper vertically above receptacle.
- Squeeze gently and steadily to form drops.
- Allow the same time between drops.
- Keep bottle at eye level to see clearly.
- Keep drops consistent in size.
This helps minimize variation and improves accuracy.
Droppers vs Liquid Syringes
While droppers allow flexibility in drawing up doses, oral syringes may provide greater accuracy and ease of measuring mL amounts. Benefits of oral syringes include:
- Ability to measure and administer precise mL doses.
- Eliminates math and conversion calculations.
- Easy to see mL markings.
- Enables measuring small amounts.
- Oral syringes are inexpensive.
However, droppers are advantageous when syringes are not available, or doses need to be given slowly or administered directly into the mouth.
Frequently Asked Questions
Why doesn’t the number of drops per mL seem consistent?
Many factors like viscosity, dropper type, drop technique and temperature affect drop size and the drops per mL ratio. Using the same dropper and technique helps improve consistency.
How should I measure thick liquids?
Viscous liquids tend to produce larger drops. Start with a ratio on the higher end of the range like 25-30 drops per mL for thick liquids.
What if I don’t have an oral syringe on hand?
When an oral syringe is unavailable, use the standard 20 drops per mL ratio for life-saving or critical medications. For other drugs, conservatively estimate 15-20 drops/mL.
Should I use the same dropper the medication came with?
Yes, using the original dropper helps maintain consistency. If transferring to another dropper, re-count the drops-per-mL ratio before dosing.
What if I can’t squeeze the dropper well?
Consider asking for help dispensing drops if physical limitations prevent proper use of dropper. An oral syringe may also be easier for administering doses.
The Bottom Line
While general rules of thumb exist for converting milliliters to drops, consider the unique liquid properties, dropper specifics and dosing situation when calculating doses. Standardize the process to improve accuracy. When precision is critical, oral syringes may provide greater reliability. But knowing approximate drops-per-mL ratios helps guide safe administration when droppers are the only option.
