I get asked ALL THE TIME, “how do you calculate fragrance oil and essential oil usage in soap?”

Different soapmakers do it differently; this is simply my opinion.

UPDATE – Please read this post.

Understanding IFRA Guidelines for Essential Oil Use in Soap

The amount of essential oil and fragrance oil used in soap should be calculated based on the base oil amount in your recipe and not the total amount of soap (oils + lye + water).

Why?

Very simple. Water amounts fluctuate in soapmaking depending on the recipe. Sometimes I make soap using a high water discount of 1.5 times my lye and sometimes I make soap using my standard water amount of 2 times my lye.

Water evaporates during the curing process and eventually the soaps would get pretty close to having the same amount of water in them. But one would have more FO/EO than the other because the extra water was included in the calculation.

Let’s look at a simple scenario. I make two batches of soap. One I’m going to pour directly into the mold and one I’m going to do a complicated swirl. To slow down swirl soap, I’m going to use more water. If I calculate the fragrance based on total recipe volume for each, it would look like this (I’m using 5% but the percentage isn’t what’s important…its the variation that we’re looking at).

Basic Pour (5% lye discount, water is 1.5 times lye)
16 oz olive oil
8 oz coconut oil
4 oz shea butter
4 oz avocado oil
4.45 oz lye
6.67 oz water

Total ounces: 43.12
5% FO: 2.16 oz

Swirl Pour (5% lye discount, water is 2 times lye)
16 oz olive oil
8 oz coconut oil
4 oz shea butter
4 oz avocado oil
4.45 oz lye
8.9 oz water

Total ounces: 45.35
5% FO: 2.26 oz

And if using “full water” your total ounces would be something like 49.8 oz (3 times the lye).
5% FO: 2.49 oz

If we were using the total recipe to calculate FO/EO usage then we would end up with THREE different amounts for a soap that will cure out to be about the same (the soap with more water would take a bit longer to cure out as the soap with less water). The three soaps would end up with three different strengths of scent.

The world is certainly not going to end if you have these fluctuations but if you are in business…a consistent (and consistently smelling) product is important and every penny counts! So it’s important to think about your FO/EO usage amounts.

So how do I calculate FO/EO usage rates in my soap?

I calculate my rates based on the amount of oil in my recipe.

My standard rate for fragrance oil is .7-1 oz per pound of oil (PPO). My standard rate for essential oil is .5-1 oz per pound of oil. Rates vary depending on the strength of your oils, but these are good starting off points. You certainly aren’t going to use .5 oz of clove or cinnamon in a soap as that would be too much.

Soap with a fragrance oil usage rate of 1 oz PPO
16 oz olive oil
8 oz coconut oil
4 oz shea butter
4 oz avocado oil
4.45 oz lye
8.9 oz water (water amount doesn’t matter)

Total oils: 32 oz
Fragrance oil: 2 oz

Soap with an essential oil usage rate of .5 oz PPO
16 oz olive oil
8 oz coconut oil
4 oz shea butter
4 oz avocado oil
4.45 oz lye
8.9 oz water (water amount doesn’t matter)

Total oils: 32 oz
Essential oil: 1 oz

If I use the recipe above for a simply poured soap with less water or a swirled soap with more water, both would end up curing with the same fragrance load once water evaporated out.

I hope this makes sense! This is one of the questions I get asked most. How do you calculate your usage rates in your recipes?

Happy Soaping!
Amanda

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