Article by: Perry Romanowski

Someone sent me a question about how to convert their formula from ounces into percentages. This is an important skill for cosmetic chemists to learn so we provide it here for anyone who might not know how to do it.

Steps to convert a formula from ounces to percentages

Step 1 — Add up the common mass terms
If you have the mass of formulas you can simply add up all of the like terms. So, if you have something in ounces, you can add up those. If you have other masses in grams, add those up separately.

Step 2 — Convert masses to grams
Since it’s easier to do calculations in metric units it is useful to convert the ounces into grams. This is done by multiplying ounces by 28.3495231. So, 2.0 ounces = 56.7 grams.

Step 3 — Convert volume measurements to masses (grams)
The challenge comes when you have some values in volume rather than mass. Volume units have to be converted to mass before you can add them. To do this, you have to know the specific gravity of a liquid. This website gives some helpful values.

Step 4 — Find the total mass of the formula
Once you’ve changed all the units to grams, you need to add up the total amount of grams. This will give you the formula’s mass total.

Step 5 — Figure out individual percentages
The next step is to figure out the individual percentages. To do this take the individual gram mass and divide it by the total gram mass.

Step 6 — Double check your figures
To make sure you’ve got everything right add up the individual percentages. They should equal 100%.

Example

See this spreadsheet example of a lip balm converted from ounces to %.  Click to enlarge

 

6 comments

  1. Angela

    Okay, this helps greatly. And excuse me for my blond airhead question here: But, after I have totaled up all the grams, how do I find out how to calculate IN 1-2% of a given recommended percentage of say… Silk amino acids PF (in liquid form, it’s concentrated), or a preservative for example? Example: My total grams is 195 grams for a recipe when adding them all up. Now I want to add 1-2% of a preservative or other special concentrated vitamin… What then??? Thanks so much – Angela

    1. Perry Romanowski

      You would just divide 195 by (100 – whatever percent you want to add) to get your total. Then figure out the percent from there.

      For example, say you have 195 grams and want to add 2% of something. 195 / (100 – 2) = 198.9
      198.9 – 195 = 3.9 which is how much you would add to get 2%

      Hope that helps

  2. Julie

    Isn’t it easier just to add up the ounces and divide each amount by the total? For example, the 4 ingredients add up to 2.8 ounces. 1.5 divided by 2.8=0.3571 x 100=35.71%

    1. Julie

      Oops, I meant 1 divided by 2.8=0.3751 x 100= 35.71% (for the 2nd ingredient).

      1. Perry

        Yes, that would work too. But I think it is important for people to put their formulas in terms of the Metric system. That’s the universal system that scientists use.

  3. nadira chase

    I think this is such useful information. Thank you for sharing this and all of the other wonderful things that you share with us.

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