Why You Should Never Measure Essential Oils in Drops

Formula Botanica teaches its students how to safely work with organic cosmetic ingredients when formulating new skincare and haircare products. Many of our students start out following fun DIY recipes that they’ve found on websites, blogs or social media. Many of our students start off wanting to measure essential oils in drops, but all of our courses strongly encourage the accurate measurement of ingredients by weight in any formulation.

We love a good DIY recipe as well, but it’s important to remember that as soon as you start to learn how to formulate professional organic cosmetics, you must start to follow professional formulation techniques. In other words, you must always measure essential oils by weight and not in drops.

Why you should never measure Essential Oils in Drops

Let’s run through our top 5 reasons why you should never measure essential oils in drops.

1. You cannot get accuracy with drops

As you’ll see from our experiments below, it is almost impossible to gain accuracy in the weight of essential oil drops. The weight of each drop will vary, depending on what oil you use, where it’s from, how it’s decanted, what its viscosity is, the dropper nozzle, human error and more.

2. Different essential oils have a different density

A drop will be a different size and weight, depending on the oil you use. Some oils will yield large drops, others will be thin and runny and pour out of the bottle in tiny droplets which don’t weigh much. So your formulation could call for 20 drops and for one oil that might be 0.3 grams, whereas for another that might be 0.9 grams. It’s simply not an accurate measurement tool.

3. Skin sensitisation risks

If you make a mistake in your counting and accidentally add too much essential oil, you run the risk of causing skin sensitisation. Many essential oils have dermal limits (we teach this in our Diploma in Organic Skincare Formulation) and these limits need to be respected in your formulation. If you get it wrong, your customer might have a skin reaction to your product. It is almost impossible to do this correctly when you measure essential oils in drops.

4. You cannot replicate your exact formulation

So now you’ve created your perfect skincare formulation and you want to replicate it again and again for your customers. How will you do that when your essential oil measurement is not exact? As you’ll see from our little experiment below, even the same number of drops from the same bottle can provide a different weight measurement.

5. You cannot scale up production

If you want to scale up your production to start manufacturing larger batch sizes, then you obviously cannot measure essential oils in drops. Imagine that your first batch is 500 grams, but within a year your orders have increased so much that you’re now working in batches of 5 kilograms. You clearly can’t just multiple the essential oil drops by a factor of 10 as this is highly inaccurate. You need to have an exact weight and percentage of essential oils in your formulation and then you can scale up production accordingly.

Our Essential Oil Drop Experiment

I recently raided my essential oil box (I have about 50 different oils) and decided to weigh 20 drops of a number of them. Here is my methodology:

• I chose 23 oils which are frequently used in skincare.
• I duplicated two of these oils (helichrysum and yarrow) by using bottles from different brands to test the difference between suppliers and I averaged the results I recorded for each brand.
• I then set up a beaker with some small jeweller’s scales and counted 20 drops of each oil into the beaker.
• After I’d measured the first round of 20 droplets, I used the exact same bottle from the exact same supplier to measure another 20 drops of the same oil.
• I then compared the weight between oils as well as the weight between the two measurements of the same oil.

What can we learn from this information? Let’s examine these results together in detail:

• The average weight of 20 drops in my experiment is about 0.6 – 0.65 grams. This does not mean that you should now assume that 20 drops = 0.6 grams, as obviously this is highly inaccurate.
• Only 20 drops of one oil (yarrow) measured exactly 1 gram. But as you can see, the second time I weighed 20 drops from the same bottle, it weighed 0.55 grams.
• Only two oils (Ginger and Palmarosa) weighed exactly the same for both measurements. This is obviously random coincidence and does not tell us anything about these two oils.

What else can we learn from these results?

1. 20 drops of essential oil does not equal 1 gram.

Or 1 millilitre. In fact, you’ll see that 20 drops of essential oil sometimes weighs as little as 0.30 grams or as much as 1.05 grams. There is no rule of thumb here. Even if you do your own experiment, you can not rely on your results to provide you with a quick, essential oil calculator converting drops to weight that you can use in the future in place of  accurate weighing.

2. You probably won’t get the same result twice.

Drops are so inaccurate in terms of weight that you can weigh the same number of drops from the same bottle of essential oil several times and you are likely to get a different result. I challenge you to try this for yourself at home too.

3.  Measurements will also vary between suppliers.

Essential oils will vary by batch, by supplier, by geographical region, by plant origin, by growing conditions, etc. etc. etc. In other words, you can buy three different batches of essential oil from three different suppliers and it’s likely that 20 drops of all three essential oils will weigh different to each other.

Why are all these measurements so different?

As I was painstakingly counting out 20 drops of essential oil each time, I had the chance to ponder this question. Here are my theories:

Human Error

The opportunity for human error is enormous. You can easily get distracted by something happening around you and you can lose count. You don’t have equipment measuring the drops for you, so you rely on your own ability to count to 20. I like to think that I’m pretty good at counting to 20, but even so I had to keep myself in check a few times as life was passing me by.

Furthermore, the viscosity of the essential oil can cause error in counting too. If the liquid has a low viscosity and drops out of the bottle quickly then you might not be able to keep up. If the liquid has a high viscosity and takes forever to drop out of the bottle, then you might become so bored that you get distracted and lose count.You’re not using any equipment to measure your drops, so the chance of you getting it wrong is big.

The Dropper Mechanism

Having tested out many different types and brands of essential oils over the years, I’ve seen many different dropper mechanisms on the caps. Some of them are great. Some of them are awful. It varies from supplier to supplier.

I found that a few of my essential oil bottles created air bubbles when I first tipped them up to drop out the liquid. The air bubble would then take along more of the liquid than normal, effectively causing 2-3 times more essential oil to drop out of the bottle. So what looks like 1 drop, may actually deceptively be several ‘drops’. Finally, the size of the droplet depends on the size of the dropper nozzle on your bottle. So you might have a large droplet if your nozzle is wide, which would then influence the weight of the drop itself.

Quality of your Scales

I used a small set of jeweller’s scales for this experiment which I bought from a well-known UK cosmetic ingredients supplier a while back. It measures down to 0.05 gram, so should be able to handle this type of experiment. Nonetheless, I wasn’t using state of the art equipment so there were undoubtedly discrepancies between the measurement readings I was taking and the actual weight of the essential oil. I was measuring very small quantities so it’s not surprising that occasionally there will be a slight discrepancy. Yet another reason to buy good quality scales.

Splashback

You’re standing over your beaker with your essential oil bottle, counting the drops as they splash into the formulation below. Because you’re dropping in the essential oil and not using a pipette or other tool to dispense the liquid, it has the potential to splash back out of the bowl/beaker/vessel that you’re using. This will ultimately effect the overall weight of the essential oil in the formulation.

The final conclusion is that you must never rely on essential oil drops if you are formulating skincare. If you follow a DIY recipe, you might still want to weigh out your essential oils to make sure you aren’t causing skin sensitisation and that you are meeting recommended dermal limits for your oils. Buy yourself a good set of jeweller’s scales (here’s an example) and stay safe in your formulations. Now if you come across essential oil calculators offering drop to weight conversions for popular essential oils, you will know from this post’s experiments that they may be inaccurate and won’t reflect the specific  gravity of your particular oil. Just to reiterate, do not be tempted to create your own essential oil calculator on the basis you will always use the same oil from the same supplier!

There are some drop calculators online aimed at helping aromatherapists create competent, useful blends for their private practice clients.  Aromatherapists’ needs are not the same as those of skincare formulators who are creating cosmetics for sale and are therefore required to have percentage formulas so their products can be safety and stability tested and, depending on the formulation, also challenge tested.

Have you ever tried to weigh 20 drops of essential oil? What weight did you measure? Share your results in our comments section below!Today’s article was by Formula Botanica Director Lorraine Dallmeier. Follow Lorraine on Twitter at @herbBlurb or on Instagram at @lorrainedallmeier.

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Lorraine Dallmeier

Lorraine Dallmeier is a Biologist, Chartered Environmentalist and the CEO of Formula Botanica, the award-winning online organic cosmetic science school. Read more about Lorraine and the Formula Botanica Team.