Calculating Soap Mold Volume


There are so many things that can be used for soap molds – cat litter boxes (new, of course), shoeboxes, and cigar boxes – okay, you get the point, boxes are great for soap molds. Once you decide on the exact size of mold you prefer, a wooden box makes an excellent mold as it is sturdy and durable.

Thoroughly lining your mold of choice with a thick trash bag will prevent leaks and allows the finished soap to slip out easily. My first experience with wooden soap molds was of the hinged variety – where the sides would drop down for easy removal of the soap. However, I found that when the mold is well oiled and lined with a trash bag it is unnecessary to have hinged or removable sides. The soap slips easily out of a solid wooden box when it is lined properly.

So, how to figure out how much soap base you need for a box or mold you already have? The calculations are simple.

Mold length x mold width x depth x .38 = ounces of soap making oils that will fix in your mold.

Some people fill their molds all the way to the top. I prefer to leave a little room as far as the depth goes. For example, if I want my soap bars to be 3 inches high, I would favor a soap mold that is at least 3 ½ inches deep. It is a personal preference.

Lets try an example with an imaginary box you’ve found in the attic. The box is 10 inches long, 3 inches wide and 4 inches deep. Let us presume you only want to fill the box 3 inches deep, instead of all the way full. This calculation for soap volume would be –

10 x 3 x 3 = 90

90 x .38 = 34.2

So, now we know that you soap mold will hold 34.2 ounces of soap making oils. This calculation for volume includes the amount of water and fragrance or essential oils that are normally used when making a batch of soap.

This math calculation will allow you to determine much soap formula you will need for any square or rectangle container you are considering using as a soap mold.

For more information on soapmaking, purchase my book, MAKING SOAP FROM SCRATCH, from aromaG’s Botanica here, or from here.