From David Fisher,
Your Guide to Candle & Soap Making.
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You are probably familiar with recipes that call for one cup of this, two tablespoons of that. You mix it up and pour it into a standard pan and cook it. You may double or halve the recipe at some point, but they're otherwise pretty standard.

However, in soap making, it’s best to use percentages for a couple of reasons:

1. It allows you to easily adjust the recipe to any size mold
2. It allows you to easily adjust the proportions of the various oils in your recipe to affect the quality of the soap.

For example, let’s say you have a recipe that makes two pounds of soap. In it you might have 1/2 cup of coconut oil. You try the recipe and the lather isn't as good as you'd like, so you'd like to increase the proportion of coconut oil. With measurements, this is hard, with percentages, it’s easy.

So, let’s convert a recipe from measurements to percentages.
We’ll start with a simple recipe-(Remember we're weighing everything, not using liquid measures.)

• 12 oz. Olive Oil
• 10 oz. Palm Oil
• 9 oz. Coconut Oil
• 8 oz. Canola Oil
• 2.5 oz. Castor Oil
• 2.5 oz. Cocoa Butter

This will make about a 4 pound batch of soap. But what are the ratios of each oil? Is this a well balanced recipe? And what if you want to make 7 pounds of soap?
Here’s what we do:

Total up the total number of ounces of oils. In this case, it’s 44. Divide each individual weight by 44 to get the percentage of that oil in the recipe.
12 oz. Olive Oil – divided by 44 = 27% (I’m rounding.)
10 oz. Palm Oil – divided by 44 = 23%
9 oz. Coconut Oil – divided by 44 = 20%
8 oz. Canola Oil – divided by 44 = 18%
2.5 oz. Castor Oil – divided by 44 = 6%
2.5 oz. Cocoa Butter – divided by 44 = 6%

So your recipe is:

27% Olive Oil
23% Palm Oil
20% Coconut Oil
18% Canola Oil
6% Castor Oil
6% Cocoa Butter
A pretty well-balanced recipe.

So let’s say you want to make a 7 pound (112 ounces) batch of soap. (Remember, that’s just the measurement of your oils. Leave room for the lye and water.) Multiply the percentage by the desired amount.

27 % Olive Oil x 112 oz. = 30.2 oz.
23% Palm Oil x 112 oz. = 25.8 oz.
20% Coconut Oil x 112 = 22.4 oz
18% Canola Oil x 112 = 20.2 oz.
And so on.

Now, whether you’re creating a recipe from scratch, or have found one online, you can both understand the proportions of the oils, and scale it to any size you like.

Happy Soaping!