How to calculate the weight of melt and pour soap
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In soapcalc, LyeCalc, or other online soap making calculators where you design whatever soap recipe you want, there is a Soap Weight (Pre-Cook) value of the whole batch before CP proccessing. If you subtract about half of the total weight of water, you will get the approximate net weight of the resulted bars of soap.
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Do you have a scale? 
MP doesn't work the same way. The amount of weight that MP soaps lose over time is negligible and takes a long time to be significantly noticeable.
MP doesn't work the same way. The amount of weight that MP soaps lose over time is negligible and takes a long time to be significantly noticeable.
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Duh sorry, was on my phone and didn't see that this was in the M&P forum.
Are you asking how to know how much base to weigh out for melting?
Are you asking how to know how much base to weigh out for melting?
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It is. But if they don't know how much MP base they used, then they probably wouldn't know.
Here is a thought:
- Weigh the mold before you start
- Melt, mix, and pour in the MP soap
- Once it is cool, weigh the whole thing again
- Subtract the weight of the mold
...no?
I did not understand the "...don't know how much MP base they used" because I do my MP based on weight: I know how much to melt to fill my mold and go from there.
To the OP: I think there is quite a bit of "try it and see" kind of culture
Sidenote (since I mentioned it): I use a 1/2 loaf mold and I find 660g of MP base fills it as far as I like - I think within a few mm from the top.
Also, the number 660 is a handy number because it is divisible by 5, 2, 3, 4, 6, 10, etc so math=easier (like, when doing layers). I do not cut them perfectly even, though - so they are not exactly all the same size/weight.
YMMV
For CP I fill the silicone mold with water up to the desired level and weigh the amount of water added in ml. Since solid soap is denser than water, I apply a multiplication factor of 1.1 (1.1g of ready-to-pour mixed soap for 1ml of water measured from the mold) to the weight of measured water in mold. Then I adapt the recipe by proportionally scaling the weights of the components in the recipe until I reach the thus measured weight of the composition that will completely fill the silicone mold. In this way, I do not waste the materials used.
Eg. 1000 ml water * 1.1 = 1100 g. The Soap Weight (Pre-Cook) in recipe is 1,234.92 g. 1100 g / 1,234.92 g = 0.89. Then I multiply every weight in the recipe with this value to obtain the ideal weight of the ready-to-pour mixed soap neccessary to fill the mold.
The bar is still warm. The final stage of gel phase. I tapped the warm gel gently with my finger. The "finger test". No skin irritation. I don't want to use my tongue and lose my sense of taste.
Eg. 1000 ml water * 1.1 = 1100 g. The Soap Weight (Pre-Cook) in recipe is 1,234.92 g. 1100 g / 1,234.92 g = 0.89. Then I multiply every weight in the recipe with this value to obtain the ideal weight of the ready-to-pour mixed soap neccessary to fill the mold.
The bar is still warm. The final stage of gel phase. I tapped the warm gel gently with my finger. The "finger test". No skin irritation. I don't want to use my tongue and lose my sense of taste.
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You cannot accurately weigh anything -- molds, bars, base, etc -- without a scale, hence why I asked if they have a scale. If they have a scale, they can simply weigh the finished bar without any fuss at all whatsoever. If they don't have a scale, they need one 
MP soap is 1:1 to water. If you fill a mold with water and then weigh the water, that's how much base to use by weight. CP measurements do not apply here.
MP soap is 1:1 to water. If you fill a mold with water and then weigh the water, that's how much base to use by weight. CP measurements do not apply here.
You cannot accurately weigh anything -- molds, bars, base, etc -- without a scale, hence why I asked if they have a scale. If they have a scale, they can simply weigh the finished bar without any fuss at all whatsoever. If they don't have a scale, they need one
I answered here inadvertently, reading only the question and not the title. This is why I wrote about the CP and not the M&P.
You are right, a scale is absolutely necessary.
In general, nothing is impossible in this world. How to weigh things without a scale? The Fulcrum method using objects of known weight, the method of using water displacement using the Archimedes Principle or the use of graduated vessels, etc. But the level of approximation is high and in soap making, regardless of the method used, precise measurements are required.
But she is asking about M&PFor CP I fill the silicone mold with water up to the desired level and weigh the amount of water added in ml. Since solid soap is denser than water, I apply a multiplication factor of 1.1 (1.1g of ready-to-pour mixed soap for 1ml of water measured from the mold) to the weight of measured water in mold. Then I adapt the recipe by proportionally scaling the weights of the components in the recipe until I reach the thus measured weight of the composition that will completely fill the silicone mold. In this way, I do not waste the materials used.
Eg. 1000 ml water * 1.1 = 1100 g. The Soap Weight (Pre-Cook) in recipe is 1,234.92 g. 1100 g / 1,234.92 g = 0.89. Then I multiply every weight in the recipe with this value to obtain the ideal weight of the ready-to-pour mixed soap neccessary to fill the mold.
View attachment 72419
The bar is still warm. The final stage of gel phase. I tapped the warm gel gently with my finger. The "finger test". No skin irritation. I don't want to use my tongue and lose my sense of taste.
katie01
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I just got my scale today, so this will definitely help.You cannot accurately weigh anything -- molds, bars, base, etc -- without a scale, hence why I asked if they have a scale. If they have a scale, they can simply weigh the finished bar without any fuss at all whatsoever. If they don't have a scale, they need one
MP soap is 1:1 to water. If you fill a mold with water and then weigh the water, that's how much base to use by weight. CP measurements do not apply here.
