April 20, 2013
- Essential Oils: Measuring % Concentrations and Fractions of Milliliters
Essential Oils: Measuring % Concentrations and Fractions of Milliliters
We're frequently asked "how much essential oil should I use in this formula"? And we give some commonly used range of percent concentrations. Through testing, however, we've realized measuring the amount of essential oil for this is a little more complex than one would think.
The reason being is that each essential oil has a different number of drops per unit (we use milliliters, which we'll use to explain the calculations here) and each essential oil has a different number of drops per milliliter.
When a recipe, or your blending wishes, call for a particular % concentration of essential oil in a carrier (this is often the case in skin care formulas), the calculation can be made like this:
Since there are approximately 30 milliliters in one ounce (the typical unit of a blend with a carrier is one or more fluid ounces), we can easily figure the number (or fraction of) milliliters required. For a 5% concentration of essential oil in one total ounce of blend, we use 0.05 x 30ml = 1.5ml. For a 1% concentration, its 0.01 x 30ml = 0.3ml.
Great, so how do we measure that? Easy if you have to measure 1.5ml and you have a pipette with 1/2ml graduations. But 0.3ml? Unless you have a pipette marked with 1/10th ml graduations, you'll have to count drops. But how many drops IS 0.3ml?
It's not widely known that each essential oil dispenses a different number of drops per milliliter. The number varies widely: using a pipette or eye dropper that dispenses 20 drops per ml of WATER, you'll find there are nearly 50 drops of some essential oils per ml.
So to be accurate, you want to know the number of drops per ml of each oil you're measuring. And we've measured the number of drops per ml of each essential oil currently in stock at Ananda, and put it all together in this table. So to measure 0.3ml of an essential oil like High Elevation Lavender, which has about 40 drops per ml using a standard glass eye dropper or pipette, one multiplies 0.3 x 40 to get 12 drops.
This difference is due to a factor called 'cohesion', which is how strongly the molecules in a liquid stick together. Water has a fairly high cohesion, so it takes a weightier drop to separate from the liquid still in the pipette. Essential oils in general have lower cohesion, likely because there's so many different molecules (venturing into unknown territory here :) that they don't pack together so closely like H2O.
The table will help you measure small amounts of essential oil when you're working with a volume, rather than already being given a number of drops for a recipe. We hope it helps!
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