# Problem with mold sizing

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#### MickeyRat

##### Well-Known Member
I like the fact that you thought of providing a method to put in the mold size and calculate the size of the batch but, it doesn't appear to be working right now. I have some new molds (10 X 3.4 X 2.5) and put in the size. The calculator correctly calculated the batch size as 34 oz. (963.88 gms) but, it didn't use that to size the recipe. It sized the recipe at 663.49 gms.

#### dixiedragon

##### Well-Known Member
I'm thinking the 963 grams is the total recipe and the 663 is the weight of oils? 2/3 of 963 is 642, which is pretty close.

#### MickeyRat

##### Well-Known Member
I'm thinking the 963 grams is the total recipe and the 663 is the weight of oils? 2/3 of 963 is 642, which is pretty close.
I didn't try to determine where the 663 came from. I think you're right. That is what the soap calculator is doing but, I don't think that's the right way to do it. In the past, the way I've determined how much oil to use to fill a given mold in ounces is to take the volume of the mold in cubic inches and multiply by 0.4. If you take my 10 X 3.4 X 2.5 mold and run that calculation, you get 34 ounces and that's what the soap calculator got but, the calculation is just for the oil, not for the total recipe. I've used the molds now and had I trusted the soap calculator rather than my own calculations, the batch would have been much too small.

This is a nice feature but, I don't think it's properly implemented.

#### Dawni

##### Well-Known Member
Strange.. I've never had that problem and I've been using the calc for months.

I just went to the kitchen and measured my mold and tried the calc and it gave me more or less what I know this mold holds, 1200 grams. If I had gone further and chose some random molds I'd get oils total of roughly 750 grams.

Or am I not getting what the issue is? Haha

#### MickeyRat

##### Well-Known Member
Put in some oils and look at the total weight of the oils in the recipe generated. My observation is that it does calculate the proper weight for the oils but, in the recipe that isn't the oil weight it uses. The oil weight in the recipe will be the oil weight it calculates minus the weight of other ingredients. In other words, while the calculated weight is correct for the oil, the recipes uses that weight as the total weight of the soap.

I have to admit that if I wasn't using new molds, I wouldn't have run across this. I had already calculated what the oil weight should be and the weight in the recipe was way off.

#### earlene

##### Grandmother & Soaper
We have to remember that the calculations we find on the internet for determining how much oil to use in a specific mold is based on the assumption that we will use the default setting of the lye calculator (SoapCalc or similar default), which means the water weight default is factored in.

I don't know what the factors are for this calculator, and how it compares to the standard calculations as I haven't kept up with all the discussions here. But for all calculators, if you change the water amount via the settings within the calculator, that will also change the total batch weight, therefore the volume going into any given mold is going to change.

I have used the calculations by measuring my molds & doing the math to determine the oil amount, then using a lye calculator with that total amount of oil, and come up with different results. It usually seems to be based on my own manipulations of to the water amount or lye concentration. Although a couple of times I ended up with too much soap batter, most of the time, changing the lye concentration meant I didn't have enough batter to fill the mold.

So that's one thing to keep in mind when evaluating if the calculator is giving you the total batch size you anticipate.

#### SoapmakingFriend

Mold Calculations at SoapMakingFriend use approximate Formula Like other calculators , we are going to consider specific gravity of all ingredients on a next update to get 100% accuracy with mold size calculations and better handle volume units .

Thank you!

#### MickeyRat

##### Well-Known Member
Mold Calculations at SoapMakingFriend use approximate Formula Like other calculators , we are going to consider specific gravity of all ingredients on a next update to get 100% accuracy with mold size calculations and better handle volume units .
That will probably yield a better result. Of course my 0.4 times the volume is an approximation for the oil weight but, it's served me well in the past. I look forward to seeing the results. Thank you for your efforts.

Supporting Member
We have to remember that the calculations we find on the internet for determining how much oil to use in a specific mold is based on the assumption that we will use the default setting of the lye calculator (SoapCalc or similar default), which means the water weight default is factored in.

I don't know what the factors are for this calculator, and how it compares to the standard calculations as I haven't kept up with all the discussions here. But for all calculators, if you change the water amount via the settings within the calculator, that will also change the total batch weight, therefore the volume going into any given mold is going to change.

I have used the calculations by measuring my molds & doing the math to determine the oil amount, then using a lye calculator with that total amount of oil, and come up with different results. It usually seems to be based on my own manipulations of to the water amount or lye concentration. Although a couple of times I ended up with too much soap batter, most of the time, changing the lye concentration meant I didn't have enough batter to fill the mold.

So that's one thing to keep in mind when evaluating if the calculator is giving you the total batch size you anticipate.
I use the 40% of volume = oil weight in ounces and it works every time.

#### earlene

##### Grandmother & Soaper
I use the 40% of volume = oil weight in ounces and it works every time.
Yes, that's what I use as well.

#### Lankan

##### Well-Known Member
I'm also having similar problem with the mold size.

my mold has a dimension of 49 cm X 6.5 cm X 7.5 cm, this gives a volume of 2388 cubic cm, which is equal to 2.39 liter (2,388 grams) of water. I've fed this dimension to the mold size into the calculator which estimates that the mold capacity to be 1653 grams (without considering the composition of the items that is going to go into the soap,). please note that 1653 grams is not the weight of the oils in the calculator output.

However my understanding is that if I fill my mold with water only, it will take up 2,388 grams of water, If i fill the same mold with coconut oil only (which has a weight of 924 grams per liter), it will be (2388*0.924) it will weigh 2,206 grams.

since most oils are less dense than water, the weight of the soap that fits the mold would be lesser than the weight of the water. However most oils seems to have density above 0.9, meaning a liter of oil would weigh at least 900 grams. Assuming that the oil and water are mixed at a ratio of 70: 30 and dissolving the lye does not add any increase to the volume or weight of the solution hence the density of the solution to remain at 1, I've calculated the following,

weight of oil portion 0.9 X 70% + weight of one portion of water 1 X 30% = weight of one portion of the the soap 0.93

weight of soap that would fit the above mold 2,388 X 0.93 = 2,221 grams

weight of oils in the soap = 2,221 * 70% = 1,555 grams
volume of oils in the soap = 1,555/0.9 = 1,727 ml

weight of water in the soap = 2,221 * 30% = 666 grams
volume of water in the soap = 666/1 = 666 ml

Total weight of the soap that would fill the mold = 2,221 grams (1,555+666)
Total volume of the soap that would fill the mold = 2,393 ml (1,727+666)

I know this is subject to number of assumptions including the change of density and volume of lye solution after dissolving the lye in the water and any possible increase to the volume without increase to the weight due to air infusion during stick blending etc.

However, this seems to be coming closer to what would fit into my mold, instead of what is indicated in the calculator OR am I making an obvious calculation error..?

#### Yooper

##### Well-Known Member
my mold has a dimension of 49 cm X 6.5 cm X 7.5 cm, this gives a volume of 2388 cubic cm, which is equal to 2.39 liter (2,388 grams) of water. I've fed this dimension to the mold size into the calculator which estimates that the mold capacity to be 1653 grams (without considering the composition of the items that is going to go into the soap,). please note that 1653 grams is not the weight of the oils in the calculator output.
I haven't finished my coffee this am, so I could be wrong, but this is where I think the problem may lie. A "volume" of centimeters won't work. I'm terrible at grams and liters, but I'll convert your metric to my US measurements and see if that is the issue.

##### Well-Known Member
The calculator has been like this from the start, I've mentioned it in previous posts but nothing has been done to remedy it. Just used it today for a batch. If you put in the mold size, in my case 28cm x 16cm x 6.5cm it gives a mold capacity of 2015g, which it gives total oils 1384g, water 392g and lye 196g giving the total 2015g. If you blindly followed the amounts given you would end up with a short batch. 28x16x6.5 gives a volume of 2912, 900g more than the calculators calculation!
What you have to do is put in the mold size and your oil amounts and then turn off the "resize your recipe to fit mold size" and the correct calculation is made to your recipe, in my case to 2932.9g.
I'll ask again, can anyone explain why it does this?

#### Lankan

##### Well-Known Member
I haven't finished my coffee this am, so I could be wrong, but this is where I think the problem may lie. A "volume" of centimeters won't work. I'm terrible at grams and liters, but I'll convert your metric to my US measurements and see if that is the issue.
In Metric system the volume, weight and the length are interlinked. 1,000 cubic cm of water = 1 liter of water = 1 kg of water.

That's the conversion I've used. If my mold has 1,000 cubic cm it will hold 1 liter/1 kg of water. Instead, if I fill the same mold with coconut oil, the same mold will hold 1 liter of oil which will weigh 924 grams. that's the logic.

Only vague area in this calculation is that when we dissolve lye or any other solids in water or oil, the increase in volume will not be the sum of volumes of water and solid. Generally it will be less than that however higher than the initial volume of the liquid.

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#### Yooper

##### Well-Known Member
In Metric system the volume, weight and the length are interlinked. 1,000 cubic cm of water = 1 liter of water = 1 kg of water.

That's the conversion I've used. If my mold has 1,000 cubic cm it will hold 1 liter/1 kg of water. Instead, if I fill the same mold with coconut oil, the same mold will hold 1 liter of oil which will weigh 924 grams. that's the logic.

Only vague area in this calculation is that when we dissolve lye or any other solids in water or oil, the increase in volume will not be the sum of volumes of water and solid. Generally it will be less than that however higher than the initial volume of the liquid.
Thanks for explaining- I emailed the developer to have him look at this more thoroughly, but what I suspect is the metric system and the US system are so different that the formula may have to differ, although I've never heard of that before. If I use "my" routine .40 of the volume as the weight of the oils with US measurements, it's far different than your results. I'm no math whiz, so the developer will look at this much clearer than I can!

For example, if I take your numbers (but in inches for the mold), it works for me.

#### earlene

##### Grandmother & Soaper
As far as the math goes, the formula itself should not change, Yooper. Only the number and units of measure change. If you remove those from the equation, the basic equation would remain the same.

#### Yooper

##### Well-Known Member
As far as the math goes, the formula itself should not change, Yooper. Only the number and units of measure change. If you remove those from the equation, the basic equation would remain the same.
Yes, that's why I'm so puzzled. The developer is looking at this, and I know he's changing some things to be about specific gravity and that should make a big improvement.

#### earlene

##### Grandmother & Soaper
I do know that the density of a liquid is effected by the temperature and that could have some impact. And that not all oils have the exact same density. But the range is so small for the difference in oil densities, that it should make much impact for the average-volume home soaper. I suppose it would for a larger commercial operation, but I can't see it making a huge difference in a 1000-2000 gram batch, and that's about as big as I usually go for a batch of soap.

For me the biggest difference is when I change my lye concentration. I can make the same exact recipe with 25% lye concentration and it uses a lot more water than the same recipe with a 40% lye concentration. When that happens, the mold will be filled differently because the batch size is really a lot different. That's where I run into issues with the most commonly used formulas for determining how much oil to use for a particular mold. I wish I could find a formula that addresses mold volume AND lye concentration (thereby the water amount) to get the recommended oil weight in order to creat total batch size that fits the volume of the mold more accurately.

If anyone knows of a formula that addresses that, I would love to see a link to it!

ETA: And of course additives contribute to Total Batch Size. And SF would as well. I use a low SF, but if I used a high SF, that would make a difference, too.

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#### SoapmakingFriend

Thank you for your feedback ,
after some discussion we decided we have a problem in the formula used to calculate mold size from mold dimensions ,
I've temporarily disabled this feature until fixed in next release .. you are still able to use the " fit to mold size" functionality by Manually entering total mold size .

Thank you

#### Amy78130

##### Well-Known Member
I do know that the density of a liquid is effected by the temperature and that could have some impact. And that not all oils have the exact same density. But the range is so small for the difference in oil densities, that it should make much impact for the average-volume home soaper. I suppose it would for a larger commercial operation, but I can't see it making a huge difference in a 1000-2000 gram batch, and that's about as big as I usually go for a batch of soap.

For me the biggest difference is when I change my lye concentration. I can make the same exact recipe with 25% lye concentration and it uses a lot more water than the same recipe with a 40% lye concentration. When that happens, the mold will be filled differently because the batch size is really a lot different. That's where I run into issues with the most commonly used formulas for determining how much oil to use for a particular mold. I wish I could find a formula that addresses mold volume AND lye concentration (thereby the water amount) to get the recommended oil weight in order to creat total batch size that fits the volume of the mold more accurately.

If anyone knows of a formula that addresses that, I would love to see a link to it!

ETA: And of course additives contribute to Total Batch Size. And SF would as well. I use a low SF, but if I used a high SF, that would make a difference, too.
Here’s a link that explained it to me! L X W X H then multiply your total by .4

https://www.thesprucecrafts.com/calculate-amount-of-soap-for-mold-517198

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