What’s in a drop – a guide to measuring essential oils for the home user
Whether you look online in books or use other resources for your essential oil recipes, you will inevitably see essential oils being measured in drops.
But what exactly is a “drop”?
How much essential oil is a drop?
How many drops are in a bottle?
What exactly do we mean when we refer to a drop of essential oil?
It may not seem it from most recipes but the reality is that what a “drop” is can vary quite a lot.
So I tend to advise that you will get between 20 and 30 drops per millilitre of essential oils, which equates to around 200 to 300 drops in a 10ml bottle of essential oil.
Now that may seem like a big range – especially when you look at the potential number of drops in a bottle! And it goes to show just how imprecise a drop can potentially be.
What makes a “drop” and how big a “drop” is can vary depending on a number of factors including –
- The viscosity of the oil – or how thick it is. Thicker oils will tend to form larger drops than thinner oils. They are “stickier” if you like and will tend to cling to the bottle, the dripolator and the other molecules in the essential oil
- The diameter of the opening in your dropper or dripolator – larger apertures will form larger drops. (Larger holes have an advantage when dealing with thicker oils as they make it easier to dispense – albeit in bigger drops!) Drops from fine pipettes will tend to be smaller, eye droppers are often bigger, and the dripolator plugs in essential oil bottles can vary a lot from brand to brand
- The specific gravity (or relative density) of the essential oil. Not all essential oils weigh the same when you compare identical volumes..
Do you remember the old riddle – which is heavier – a pound of lead or a pound of feathers? The answer is they both weigh the same. BUT the pound of feathers will take up a much bigger space than the pound of lead.
Conversely, if you were to take a bucket of lead and a bucket of feathers, then obviously the bucket of lead would weight a lot more.
The same applies to essential oils – although the differences are less dramatic than the lead & feathers example, each essential oil will have a different density and therefore a different specific gravity. So a drop of each will weigh differently.
If you were to look at water – then 1 gram equals 1 millilitre. But with essential oils the same does not apply. You will generally need more than 1 millilitre of essential oil to equal 1 gram. But how much more will depend on the specific gravity of each individual essential oil.
Fun fact – Because essential oils have a specific gravity of less than 1, they tend to float on water.
- Temperature – some essential oils can become quite thick (some almost solid) in colder conditions and therefore make for larger drops.
Even given the same apparent conditions and using the same essential oil, you can still get variations in drop size.
It is for this reason that many aromatherapists and most formulators will tend to use weights rather than drops – grams and milligrams. When you want to be able to reproduce a formula accurately, you need to use a measuring system that will give consistent results. Weight measures will do this – drops will not.
To illustrate the differences, I ran a little experiment.
(Disclaimer – this was a quick test and may not stand up to full scientific rigour!)
I took 3 different essential oils and for each I did the following –
I measured 1ml in plastic disposable pipette, transferred to a glass beaker and weighed the contents. I then used the same pipette to measure the number of drops in the 1 ml, by dripping the same oil using the pipette into a beaker until it reached the same weight, counting the number of drops.
I then repeated this using the bottle with dripolator plug, again counting the number of drops to reach the same weight.
These are the results –
|Oil||1ml weight||No of drops – pipette||No of drops – dripolator|
Now this is a rough experiment! But you can see from this that the numbers are close but not identical. And I would assume there may be some variation if I repeated the experiment on another day or in a warmer or cooler room.
So this illustrates why general quantities given in recipes for homes use tend to be ranges or approximates of the number of drops.
However for all their shortcomings from a professional perspective, drops are still the easiest method of measurement for home users, and sufficiently precise for most situations. Afterall, you don’t want (or need) to weight the number of drops to go into your diffuser on a daily basis. A range is perfectly acceptable in this situation.
To be safe, and as a general rule I tend to recommend working with a formula of 20 drops equalling one ml. This gives you some room to allow for variations in drop size without making your formula too concentrated, (and also gives you some leeway if you slip up and accidently add an extra drop!) Plus if you find your formula needs a little extra, you can add without issue – you can’t take a few drops out if you use too much!
So go ahead and measure your essential oils by the drop at home. At the end of the day, whilst for the purposes of professional formulation or clinical use, weights may be preferred, for home use, drops are much easier, more accessible and sufficiently accurate for most people and most of the uses you are likely to put them to at home.