Resizing and Converting Soap Recipes

Have you ever seen a soap recipe that makes much more soap than you need and you want to scale it down and aren't sure how? Or have you seen a recipe expressed in percentages and wondered what that means and how to translate it into ounces or grams?

A few weeks ago, a reader asked me how to do those very things, and it got me thinking about writing a blog post dedicated to those questions.

Percentages and conversions can be confusing, especially in the beginning. Different soapmakers may do different things, but here is how I convert recipes into something I can use.

First of all, it's important to know how much soap your mold will hold. A three-pound mold holds three pounds of soap. Makes sense, right? But how much of that is oils and how much is water? How do you know how much oil to include in your recipe so that, when added with the lye solution, you end up with three pounds of soap?

And what if you aren't sure how much soap your mold holds? Let's say you're using a lined shoebox, a silicone baking mold, a homemade mold, or even a wooden box that was once packaging for something else. How do you determine the mold's capacity?

L x W x H

One thing you can do is fill your mold with water and weigh the water. A scale with a tare function is good for this. (The tare weight is the weight of the empty container. The tare function on a scale allows you to reset the scale to zero after you have placed the container on the scale, thereby weighing only the contents of the container once they are added.) Place your mold on the scale, press the tare button, and then add water until your mold is filled to your preferred level. Note the weight of the water to get an idea of how much your mold will hold.

Of course, the water method works better with some molds than others. You wouldn't want to pour water into a wooden mold unless you lined it with a plastic bag or something first. If it isn't convenient to use water, or if you just don't want the hassle, here is a handy formula you can use to help determine the capacity of your mold:

L x W x H x 0.4

This formula will give you a good idea of  the OIL WEIGHT in ounces for your mold, which is helpful since soap recipes are built on oil weight. The lye solution (water + sodium hydroxide) will account for the rest of the weight, filling your mold to capacity.

For example, my three-pound wooden mold has the following dimensions: 10 inches in length, 3.5 inches in width, and 2.75 inches in height. To fill the mold all the way to the top, I would need a recipe with 38.5 ounces of oil. If I want to leave a quarter-inch of space at the top to allow for texturing, a lid, etc., I would need 35 ounces of oil (10 x 3.5 x 2.5 x .4).

If the maths make you sad, the Summer Bee Meadow soapmaking calculator will resize a recipe based on the dimensions of your particular mold. Just take a recipe, plug it into the lye calculator, and then use the recipe resizer after you've calculated the recipe.

Here's an example. Let's say that I found a great-looking soap recipe, like this Beginner 6.5 Pound Soap Recipe from Teach Soap:

5 oz. Canola Oil
5 oz. Castor Oil
32 oz. Coconut Oil
32 oz. Palm Oil

11 oz. Lye (5% superfatted)

24.4 oz. Distilled Water

This recipe makes way too much soap for my three-pound mold, so I'm going to need to resize it to fit my mold's dimensions. Let's go to the Summer Bee Meadow soapmaking calculator and plug in those numbers:

After entering the oil amounts and desired superfat, I will hit the "Click Here When Done" button to get the full recipe, including lye and water amounts. (It's always an excellent idea to double-check a recipe that you find online or in a book or wherever by running it through a lye calculator, just to make sure that it is correct.)

 

So there is the the complete recipe. It's way too big for our mold, though. Right below the recipe is the "Soap Recipe Resizer" area where I can specify the dimensions of my mold and generate a new recipe based on those figures:

 

I selected "Rectangular Mold" and plugged in my dimensions. Notice that I opted to use 2.5 inches for the height to allow for a quarter-inch of space at the top. Here is the recipe resized to fit my mold:

 

Voilà! There's my new recipe, resized to fit my particular mold. (And note that the oil weight is 35.60 ounces, which is pretty close to the 35 ounces of oil I figured I would need by multiplying 10 x 3.5 x 2.5 x .4.) This resized recipe should be about right. Notice that it does give a total recipe weight of 3 pounds, 5.41 ounces. If you have a little left over, just pour it into a small mold. You can tweak the numbers later if you find that you need to.

Tip: This recipe is in ounces, but I recommend measuring ingredients by weight in grams for better accuracy. Summer Bee Meadow is working to implement a grams calculator. (SBM also has lots of other great stuff on its website, so do check it out. Also, Steve is working on a new interactive website, SBMCrafters.com, and it should be lots of fun when it is fully implemented!) In the meantime, you can find handy ounces-to-grams conversion calculators online. Or you can plug your recipe into the SoapCalc lye calculator, which will calculate your recipe in pounds, ounces, grams, and percentages.

Speaking of percentages, what the heck does it mean when you see a recipe that looks like this?:

45% Olive Oil

29% Coconut Oil

17% Palm Oil

6% Shea Butter

3% Castor Oil

Basically, this is a breakdown of the proportions of each oil in the total amount of oils. Olive oil is 45% of the total oils, coconut oil is 29% of the total oils, and so on and so forth. 

Why would anyone express a recipe in percentages instead of ounces or grams? Well, the great thing about percentages is that it can be adapted for any recipe of any size. If a recipe is expressed in ounces or grams, you would have to either visit the resizer calculator, or figure out the percentages and then translate the percentages into a recipe that fits your needs.

But how do you translate those percentages into a recipe?

Let's say that I want to try out the above recipe in my 3-pound wooden mold. I already know that I need about 35 ounces of oils to create a soap recipe that will fit nicely into it. With that information and the recipe's percentages, I can go to SoapCalc and easily create a recipe that will work for my needs:

I am using sodium hydroxide, so I selected NaOH in field #1. In field #2, I entered 35 ounces for my oil weight, since that produces a perfect-sized recipe for my three-pound mold. I am going to leave the water at 38% of the oil weight (which is the "full water amount," something you may hear soapmakers say), but field #3 allows me to specify a water discount if I so desire. In field #4, I set my superfat at 5% (the superfat is the amount of unsaponified oils that are sort of free-floating in your bar, making the soap more nourishing). Here, I can also specify a fragrance oil usage rate, which is .50 ounces per pound by default. I'm not going to worry about field #5, but I could play with soap qualities there if I wanted to. To create my list of oils, I select an oil from the "Oils, Fats, and Waxes" list and hit the "+" to add it in field #6. I can express each oil in either ounces or percentages. I'm using percentages here. (I could also use grams or pounds, too, but I'm going to stick with ounces and percentages for now.)

Once all of that is done, I click on "Calculate Recipe" and then "View or Print Recipe" to get the full recipe, including lye and water amounts:

And there it is. A recipe that is perfect for my 3-pound mold and shows me all of the measurements in pounds, ounces, grams, and percentages. It even shows the weight of my soap (3.398 pounds), which should be just about right. SoapCalc also provides all kinds of interesting info, such as the qualities of the particular recipe.

Another neat thing you can do? You can reverse-engineer a recipe with SoapCalc to figure out the percentages and then adapt it to your needs.

Let's use the same recipe, but instead of it being presented in percentages, let's say that it looked like this:

36 oz. Olive Oil

23.2 oz. Coconut Oil

13.6 oz. Palm Oil
4.8 oz. Shea Butter

2.4 oz. Castor Oil

To make it fit into my 3-pound mold, I can plug those numbers into SoapCalc, find out the percentages, and then do what I did above and plug those percentages into a recipe of my desired size.

Here's a visual. There are 80 ounces of oil total in this recipe. I enter the ounces of each oil in field #6:

After calculating the recipe and hitting "View or Print Recipe," I can see the percentages for each oil:

Now I can recalculate the recipe using 35 ounces of total oil weight and the percentages of 45% olive oil, 29% coconut oil, 17% palm oil, 6% shea butter, and 3% castor oil, just as I did above earlier to make it fit into my 3-pound mold.

Cool, huh? And SoapCalc is more than just a lye calculator - it has some great tips, links, and videos, too.

So that's how I convert my recipes. What tips and tricks do you have for resizing your soap recipes?

(Oh, and if your head hasn't already exploded, check out this Soap Queen blog post to learn more about converting usage rates, parts and ratios, and percentages!)