# Converting ml Mold Size to Batch Size

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#### BrewerGeorge

##### Well-Known Member
I realize there is a large, sticky thread about this subject, but not yet knowing this forum's etiquette about posting to sticky threads I am defaulting to that of my brewing forum. That is posting a new thread and letting the moderators decide if the info is "worthy" of joining the sticky. If that is not the way things are done around here, please let me know and I'll conform in the future.

I have read the sticky thread fully and understand how to calculate the weight of oils for regular-shaped molds (though I am still a bit shaky on how to account for differing lye concentrations.) My uncertainty is around irregular molds. Since it would be relatively easy with the scale to find the volume of any mold by weighing it while filled with pure water, I think that is the best starting point for me personally and I'm hoping that someone can confirm my understanding from the sticky.

I believe that I should be able to find the total grams of oils needed to fill a given mold by multiplying its volume in ml by 0.7. Is this correct? If so, at what lye concentration is that correct?

Also, soapcalc gives a result titled, "Soap weight before CP cure or HP cook.' Is that number useful at all in accounting for differing lye concentrations?

#### IrishLass

Staff member
Moderator
Hi Brewer George- for future reference, yes- it's best to just start a new thread. We're thinking of locking all our stickies down to eliminate the confusion.

Round and decorative molds are a bit math-tricky for sure, so I ended up doing things a different way with those kind of molds that doesn't involve using a math equation.

Basically, I just filled the decorative mold cavities up with water and then poured the water out into one of my measuring cups that I use for soaping, and then I took note of the volume (not the weight). It was easier for me to go at it the volume way, because through trial and error mixed with my meticulous/obsessive note-taking over the years, I happen to know how much volume/cups of batter different weight-sizes of my batches make at certain lye concentrations, and so I'm able to easily figure out how big of a batch to make weight-wise that will give me the proper amount of batter that I need volume-wise to fill my decorative molds. I hope that made sense.

Hopefully, those who use different concentrations for different batches and who have figured things out the weight way using a math calculation will chime in soon.

IrishLass

#### BrewerGeorge

##### Well-Known Member
....

Basically, I just filled the decorative mold cavities up with water and then poured the water out into one of my measuring cups that I use for soaping, and then I took note of the volume (not the weight). ...
That's basically what I was thinking, too. But rather than trying to juggle a floppy silicone mold, I was planning to take advantage of the fact that a gram of cold water is a milliliter and just weigh the whole thing full.

#### snappyllama

##### Supporting Member
For irregularly shaped molds, I fill with water and pour into one of my regular molds whose volume is already known. Then I estimate to get approximate volumes. I keep some individual molds nearby when I'm soaping in case I miss calculate. I'd much rather have a bit too much than not enough. Sometimes maths just fail me... I made a cake this weekend and ended up with enough overage to make five cupcakes.

#### The Efficacious Gentleman

As the rule of thumb is centimeter WxLxHx0.7 (for metric, or 0.4 for imperial) it is essentially cubic centimeter volume x 0.7.

I find that volume and soap is a funny thing. Thinking back to my last salt bar, I added in a lot of salt to a batch of oils that would fill my mould - it was more than 50% but we'll say 50% for arguments sake. So in my logical head I should have had a lot more batter, overflowing the moulds. But the volume only changed slightly.

Now, if we soap at 30%, or 31 or 32 and so on, does the volume of the batter change accordingly? I don't think it is a direct 1:1 increase in volume as the weight increases.

That said, there might be times when you need to have an overflow mould standing by

#### Susie

Supporting Member
I always, always, always keep overflow molds handy. Even when I have made the same recipe a dozen times. You never know when you will make a weighing "oops", and need a mold. And the very time you think you won't need one, you get to scramble around and find one, then make sure it is clean, then hope your soap batter has not solidified in your bowl. Better to have it and not need it than need it and not have it.

#### nsmar4211

##### Well-Known Member
I've made the exact same batch and had it fill differently because I poured the mold 1/16th of an inch differently..... I err on the overage size and have my little silicone fun molds to fill and use as testers . I've been doing the "fill with water" thing so far myself.