How to Dose Essential Oils in a Formula

In connection with this previous post, today's subject details a bit about why precision is so important when making formulas for skincare products.

We're going to touch on something some DIY'ers hardly even give a thought  –  how to dose essential oils in a formula.

You: Seriously, Lise? We need lessons in counting drops?

Me: You mean you're measuring by the drop?

By the Drop? Please Stop.

A lot of people measure out essential oils by the drop when making a product for personal use (or in very small portions for friends and family).

It's totally understandable, "It's a super small batch and it's just a few drops."

Nevertheless, it is inaccurate to measure essential oils by the drop.

Why This Even Matters

You might be shaking your head by now and wondering why this matters at all.

I understand.

It really sounds a bit like overkill.

But picture this little scenario:
Let's say your family and friends have fallen in love with your product and demand is growing. Wonderful! You need to make bigger batches to accommodate everyone. Maybe you are also now considering selling your product through an online shop or at markets.

If your formula is not 100% precise, then you have no idea what percentage essential oil is in your product. If you upsize your formula by simply multiplying the drops of essential oil, you might exceed recommended dosage and your product may even cause harm to a customer.

As tempting as it might be to assume all essential oils weigh the same, this simply isn't so.


Because of a little something called density.

That Little Something Called Density

Every essential oil (and every carrier/fixed oil) has its own density. You can check out the nerdy details about what density is right here, but this picture kinds of explains it all.

See how the different oils in this graduated cylinder are 'layered' and not mixing? That's because each oil has a different density.

Even if you measure out the exact same volume of a few different oils and weigh each one, and even if you have been super-duper careful and poured up EXACTLY one teaspoon, the oils will not weigh the same unless they happen to have the same density.

This is why it is not accurate enough to measure essential oils (or any oils) by volume.

Ingredients – even single drops of essential oil – should always be measured by weight.

Putting it To the Test

Lorraine Dallmeier – Owner and Director of Formula Botanica – did her own comparison test. She measured the weight of 20 drops of several essential oils and recorded the results.

The difference in weight was a real eye-opener. Her test showed twenty drops weighed as low as 0.35 grams and as high as 1.05 grams.

Now, imagine upsizing your essential oil blend for a batch production by counting drops. That could be asking for a bit of trouble, couldn't it?

Today's tip: always measure by weight!

Read Lorraine's post and test results right here.

Which Scale

Since you ask: I use a jewelers scale for measuring minute amounts. Here's the one I have been using the last couple of years.

Do Tell

Are you a 'by the drop' person or are you measuring your EO's by weight?

Density Illustration courtesy of Wikimedia Commons


Signe said…
Well, I am "by the drop" person, but I totally understand and am aware of that knowledge that when you are making bigger batches and selling your products you need to measure everything by weight. But that photo you shared is very informative, thanks for that! I knew oils have differences, but I didn't realize that they can be so huge. That reminds me that when I'm making soap I need to mix oils properly before adding lye - otherwise my soap might not be safe to use.
María Zamora said…
I measure by the drop as well when making creams, as I make small batches (50-100 g). But for soap making, weighting oils in a precision scale is piece of cake.
I have to confess that I'm becoming lazy when I make soap, and I tend to use 10 ml essential oils/fragrances per 500 g of oil (not soap, oil), but that's just me.
Paula M said…
I have the exact same scale and it's the one I recommend to my students. Soaps always weight! Creams, I use drops because we make about 180g at a time. If I was selling a product I would use weight for everything.
Lise M Andersen said…
@Signe - Ooh I'm glad to be of help! :)

@María - When I am doing something for personal use, I am also a by the drop person. All of my earlier scent blends were created by the drop. I'll bet what you call 'getting lazy' is mostly because you have been doing this so long you know exactly what you're doing. That's not lazy, that's experience! :)

@Paula M - Isn't it the greatest little scale? I do what you do as well - smaller batches for personal use, I'm a by the drop person. :)
J.S. Gates said…
Hi Lise,

Thank you for the informative post! I know that Essential oils should only be about 1% to 2% of the total product blend. I've started making 42g lotion bars in semi-medium batches, so blending 33 1/2 ounces of butter at a time and then pouring into mini molds. I add in 7g of essential oil to my 33 1/2 ounces of butter and I've had pretty great results thus far. Am I on the right track when it comes to weighting out my essential oils at an appropriate dilution? Or could I add a bit more essential oil to the overall batch?

Thank you!!
Lise M Andersen said…
Hey there J.S.Gates - Thanks for your comment. It worries me a bit that you seem to be using both the metric and imperial measuring methods at the same time. Personally, this would confuse me to no end.

Let's do the math and have a look:
33,5 ounces equals 949,7 grams. Let's round up to 950 grams.
1 % of that is 9,5 grams.
You are adding 7 grams so it looks like you are keeping within the general safety limits with your essential oil amount.
Of course, the 1-2% max is a general rule. Some essential oils have a much lower recommended max dosage, so you'll have to look at the recommended percentages of each of the oils in your blend to be sure. Best of luck with it!
J.S. Gates said…
Hi Lise,

Thank you! Yes when I'm formulating I measure in ounces so when I was going through my notes last night I tried to convert everything to grams. Sorry I missed one and had you do all that math! But it looks like I should just convert over and measure in grams in the first place!
Lise M Andersen said…
Thanks for clarifying J.S. Gates! :)
Katie said…
Hi, I am currently a by-the-dropper, but I do plan on purchasing a jewelry scale to convert to weight. My question is about diluting by weight vs. volume. It seems to me that most of the safety guidelines were developed in relation to volumes, so is it safe to assume that a 2% dilution by volume is the same as a 2% dilution by weight? Thank you!
Lise M Andersen said…
HI Katie - A cosmetics formula is always measured by weight. It is not safe to assume 2% by volume is the same as 2% by weight- stick to weight and you will always know what you are working with. :)
Abe said…
Each Essential Oil has its own density and it matters a lot in cases such as making suppositories. I have a similar scale as the one shown here, but it isn't accurate enough and I've learned it the hard way!

The formula I follow contains among many E.O 10 mg of Pogostemon Cablin and 25mg of pistacia lentiscus. The scale should be precise to the milligram. Accuracy will determine whether the suppositories will represent a health hazard or be inefficient because it's used internally. Such small weights can actually be smaller than a single drop.
LisaLise said…
Hi Abe - you are correct in that every essential oil has its own density- Sorry to hear you had to learn this the hard way. Thanks for your comment.