How to Work Out Percentages in your Cosmetic Formulation
I often get questions from people wanting to know how to alter a formulation they have always made using volume, or a combination of volume and weight measurements. They realise that measuring in cups and spoons is okay most of the time but find they have problems when it comes to increasing batch sizes or they find that sometimes they don’t always get the same result each time them make it.
Although there isn’t anything intrinsically wrong with using volume, it is trickier to scale up formulas and problems can arise when ingredients change form. For instance, it could be that they always bought cocoa butter in button form and then the supplier changes it to flakes or even a large solid bar; depending on the form the cocoa butter takes, could result in it taking up more or less space (volume) than other forms. This will obviously have an effect on the overall amount used in the formula and a fundamental change in the final characteristics of the end product. This is why it is always good to formulate in weight, to ensure accuracy no matter what form an ingredient takes.
It is not unusual for scientists to use volume measurements, indeed it is a practice in pharmacology especially when using measurements that are very small and impossible to weigh.
It is also less important to use volume when you are using all liquids, you can easily replicate 100ml of apricot oil and 50g of polysorbate 80 and can scale up. However, when it comes to formulating cosmetics it is not always ideal, especially when using a combination of wet and dry ingredients. For your formulation to be replicable and for scaling up purposes, it is good practice to weigh each ingredient, liquid and dry.
Using Percentages and the Metric System
A percentage is a number or ratio expressed as a fraction of 100. When we talk about percentages, we imagine that 'a whole' has been divided into 100 equal parts.
We use percentages to make calculations easier. It is much simpler to work with parts of 100 than thirds, twelfths and so on, especially because quite a lot of fractions do not have an exact (non-recurring) decimal equivalent. It also makes converting to metric systems of weighing easier.
The industry standard is to work using the metric system. It is considered the most accurate, is internationally accepted, and much easier when it comes to scaling up/increasing batch size. Using percentages can easily be converted to grams and then scaled up to kilos and tonnes.
So what is the best way to convert your recipe from volume to weight measurements and then to the metric system? The following is an easy guide to ascertaining the weight and percentages of a recipe you have always measured using volume (ml, cups, spoons etc.)
Converting your Recipe into a Cosmetic Formula
The first thing you should do is make the product as you normally would, but as you go along you should weigh and make a record of that weight. Some might suggest ascertaining the specific gravity for each ingredient, which is one way of approaching this but I personally think doing it the old fashioned way is better. When people work in volume they also rely on their observations (what the ingredient looks like in the specific vessel/container) to determine they have used the right amounts. So I think that physically making the product and weighing is going to give the greater accuracy in this instance.
Weighing your ingredients
Start by selecting the ‘grams’ setting on your scale. If your formulation requires 1 cup of cocoa butter, then weigh it and record that weight. Do this with each ingredient, regardless of whether it is liquid or solid. You will then end up with the weight equivalent for each ingredient.
Secondly, you need to calculate the total weight of your ingredients by simply adding them together. See example below.
This is a dummy formula (it will likely not make anything usable.)
Cocoa Butter 60g
Kokum Butter 20g
Sunflower Oil 40g
Rosehip Oil 75g
Vitamin E 2g
Beeswax 35g
TOTAL: 232g
You now know what each ingredient in your formula weighs and the total combined weight: 232g
Thirdly, to work out the percentage (the fraction out of a 100 total amount) of each ingredient you will need to divide each ingredient with the total weight amount, in this case 232g, and then multiply by 100. As you will see below, I have rounded to the nearest whole number. Of course you can round to one or two decimal places depending on how close to the original weight amount you want to get.
It should look like this:
INGREDIENT %
Cocoa Butter 60g /232 x 100 = 25.86 (26.00)
Kokum Butter 20g/232 x 100 = 8.62 (9.00)
Sunflower Oil 40g/232 x 100 = 17.24 (17.00)
Rosehip Oil 75g/232 x 100 = 32.33 (32.00)
Vitamin E 2g/232 x 100 = 0.86 (1.00)
Beeswax 35g/232 x 100 = 15.09 (15.00)
TOTAL: 100%
Now, add each number in the percentage column and you will have a total of 100%. You will then have to look at it, and use your judgement to see if it makes sense.
Converting to Grams
Simply put, 1% is equivalent to 1g, 5% is equivalent to 5g. In all cases 100g is the same as 100%. If you want to make double the amount you would multiply each ingredient by two. If you want to make 300g you would multiply by three and so on. If you wanted to scale up the above formula to 250g then it is easy. You will simply multiply each ingredient by 2.5 as below.
Ingredient %
Cocoa Butter 26.00 x 2.5 = 65g
Kokum Butter 9.00 x 2.5 = 22.5
Sunflower Oil 17.00 x 2.5 = 42.5
Rosehip Oil 32.00 x 2.5 = 80
Vitamin E 1.00 x 2.5 = 2.5
Beeswax 15.00 x 2.5 = 37.5
TOTAL 250g
Note on restricted ingredients
Restricted ingredients are those that need to be in the formula at a specific range or dose. They are normally things like preservatives, essential oils and fragrances. They are restricted because using too much or two little could negatively impact a formula or be unsafe at particular levels.
If you have a formulation that contains restricted ingredients (essential oils/preservatives) you may end up being over or under that recommended dose and will need to adjust. Say you have an emulsion with water and oil phases and the preservative is over or under the recommended amount you should then adjust it to the desired level. To make sure the overall formula is calculated to 100% you may want to adjust the water content.
Checking the formula
Once you have finished calculating the percentages you will then have to make the formula again following the your calculations. The formula isn’t likely to be perfect but you will have a starting point. I like to use an excel spreadsheet to do this but it is possible to calculate manually, in fact that is how I started.
Using this approach is ideal for anhydrous products but can be applied to other types of formulation. The key is to ensure that you know your ingredients well and read the data sheets of potent ingredients such as preservatives and fragrances and use your knowledge to decide the safest way to proceed.