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