Drops per mL Explained
Did you know that all drops aren't created equal? Do you know how dramatically this affects the concentration of E.O.'s in your blend?
We were perplexed to find out that the information on this topic describes a typical essential oil as having a static value for blending. Most websites and amateur aromatherapy blogs state that this drops/mL value resides at 30 drops/mL for every essential oil and extract. With a robust set of experiments we have charted all of our oils and extracts and found that our oils and extracts range greatly and we wanted to help guide aromatherapists to the understanding of this simple fact. With the physical shape of drops changing based on our physical property measurements (viscosity and specific gravity) we have seen oils that go from 25 drops/mL to well over 65 drops/mL. This will absolutely result in a large concentration percentage drift in a typical batch of blended oils.
Blending in aromatherapy is a result of the idea that essential oils, each with its own complex chemical makeup, can work together both aromatically and therapeutically. The practitioner may desire precise ratios of each essential oil, or constituents within these oils, in their final blend. Further, essential oils are commonly diluted in “fixed” (non-volatile) seed, nut, and vegetable oils, also known as carrier oils, for topical application. In this case, it is widely-held that the concentration of each essential oil be at or below a certain percentage in these mixtures for safest use.
Unfortunately, recipes for blending, as well as dilution formulas, most often indicate a number of drops for each essential oil in the blend. Many aromatherapy recipes may have, in fact, been created with specific concentrations of each essential oil in mind, but used a commonly-accepted value such as 20, 25 or 30 drops/mL. However, variations in viscosity and other physiochemical factors of the essential oils can produce large variations in drop size from a single dispenser, resulting in significant differences of essential oil concentrations than the recipe's creator intended.
Another issue that is not taken into account when formulating blends are the pipettes and droppers used to create the blends. There are countless droppers one can purchase which vary in the type of material, such as plastic or glass, the diameter of the outlet, and the pressure required to be applied to produce the drop in question. In order for essential oils and blends to be used therapeutically in a dose dependent matter, as they are intended, a standardized drop size per oil should be calculated for consistency.
Here at the Ananda Apothecary we have calculated the drops/mL for all our oils in hopes to benefit any potential blending that our customers may want to try out. No more relying on the same drops per mL value for every oil!
Using the number of drops per milliliter when figuring how many drops are required to make a particular % concentration in a carrier oil:
When creating blends, you may come across notations of % concentrations. Such as, "use Tea Tree essential oil at 5% concentration in Hazelnut for..." or "do not exceed 5% concentration total of essential oil..." How do you measure the percent concentration of an essential oil in one or more ounces of a blend in a carrier oil?
One way to measure the % concentration of an essential oil in each ounce of blend with a carrier oil is to use the number of milliliters in each ounce (30), then figure the number of milliliters of essential oil needed, and then how many drops of essential oil that is. The calculation goes like this:
- There are 30 milliliters (ml) in one fluid ounce. (Actually 29.57ml/floz, but 30 really is close enough).
- You can figure the number of milliliters of essential oil required in each ounce by multiplying the % desired concentration by 30.
- For example, 10% is 0.10 x 30 = 3ml
- 1% is 0.01 x 30 = 0.3ml, or about 1/3rd of one milliliter
- 0.5% is 0.005 x 30 = 0.15ml...and so on.
So how do we measure 0.15ml of essential oil? If the oil is High Elevation Lavender, then from the table above we see there are 40 drops per milliliter. So the number of drops in 0.15ml is 0.15 x 40 = 6 drops. This is the number of drops for a 0.5% or 1/2% concentration in one ounce of blend. 1% is, as above, 0.3 x 30 = 12 drops. To be accurate, you would add this to 1 ounce of carrier minus 12 drops, or put the 12 drops in an empty one ounce bottle, then fill the rest with your carrier (this becomes more critical with higher % concentrations -- this is instead of just adding the drops to an already measured one ounce of carrier).
Typically we're working with pipettes that are possibly marked at each 1/2 ml, or eye droppers without any measurement markings at all. Here's where we make use of the number of drops of essential oil per milliliter. It is commonly thought that there are 20 drops per milliliter, and this is true of water when using 'standard' measuring tools -- the 3ml graduated pipettes or glass eye droppers that come with certain essential oil sizes from Ananda.
However, the number of drops per milliliter of a liquid is not only affected by the dropper, but by the properties of the liquid itself. There is a property called "cohesion", which causes the liquid to stick together more or less. Water has high cohesion, therefore the drop sizes are larger and there's fewer drops per milliliter. The high cohesion requires that the drop weigh more before it separates from the rest of the liquid. Each essential oil has a different number of drops per milliliter!
So when creating your own blends and want to use a particular % concentration of essential oils, or when you need to measure an essential oil in milliliters, but do not have a measuring device, you can use the above table and simple calculations to find the number of drops you require.
Again, to find the number of drops of essential oil in each ounce of blend with a carrier, use this formula:
(The desired % concentration) x 30ml/oz x (The number of drops per milliliter from the table above). Ex: 5% of Tea Tree in one ounce is 0.05 x 30 x 41 = 61.5 drops (it's up to you to put in the extra "half" drop or not!)