how to measure soap volume for mold?

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Well-Known Member
Aug 13, 2014
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Vacaville, Ca
Hello, I have been making soap for almost a year and have decided to increase my batch size. My father made me some wood loaf molds based on measurements we saw online for a 10lb loaf mold. Most wood molds are named for their size, 2lb, 4lb, 10lb, and so on. The interier dimensions we used are 3.5" x 3" x 35". We made our mold a little taller so I have extra room on top for design and a lid. I have seen volume calculations online that say to do the following math: 3.5 x 3 x 35 = 367.5 x 0.40 = 147 ounces. My question, is that 147oz of oils or soap? I've tried doing the math on both possibilities and it is not adding up. My first time using the mold and I made a batch with 10 lbs of oils (160oz) and it made too tall of a bar which would mess up all my packaging designs so i ended up cutting a half inch off the bottom and rebatching 51oz of scraps. So my next option is to make a batch with 7 lbs of oils which will give me slightly over 10 lbs of soap. My fear now is that it will not be enough soap to fill this giant mold, lol. I've done the math on other molds to try to make sense of it and it doesnt. For example, My "4lb loaf" mold (2.5" x 3.5" x 15") that i purchased off brambleberry, using the math above, would give me 52.5oz which is 3.28 lbs. So why is it called a 4lb mold? Is that 52.5oz of oils? If so, that would produce 5lbs of soap, based on SoapCalc with 38% water and a 0.5 fragrance ratio.
Here is a thread that talks about it and all the measurements. I can't do a better job explaining so I'll just direct you there. The formula you have is to calculate the amount of oils needed, assuming full water. I think they name the molds as a near estimate of how much it holds. A 2.5 pound mold can sometimes hold 45 ounces of batter, but they still call it a 2.5 pounder.
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