# How to figure how much oil for mold.

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#### Todd Ziegler

##### Circle Z soaps
..

Just one question .. when the M&P base is in blocks, how do you know how much to melt to get the "liquid amount"? I hope that makes sense.. for example, say my mould held 100ml of water, how much solid block soap do i need to weigh out in order to have 100ml of melted soap? One would assume around 100g, but i dont know...

That may have a really easy and "commonsense" answer, but times when i've used this method, ie measuring how much water the mould can hold, i've not been totally successful, had a bit too much most of time..

Thanks very much everyone would really appreciate an answer for this
I used a wilton shot glass mold and it used 539 grams of M&P soap. I know that isn't exactly the answer you were looking for but if you look up the mold on line, you can work backwards maybe. I am not good with the math or I would tell you more lol.

#### Wyndham Dennison

##### Active Member
weigh cu inch of M&P. a cu inch of water weighs about 16 grams. 100 gram(ml) water / 16 =6.25 cu in (x) the weight of m&p should get close or I've messed up the math

#### shunt2011

##### Moderator Emeritus
Moderator Emeritus
I used a wilton shot glass mold and it used 539 grams of M&P soap. I know that isn't exactly the answer you were looking for but if you look up the mold on line, you can work backwards maybe. I am not good with the math or I would tell you more lol.
This poster you quoted hasn’t been here since 2008.

#### Wyndham Dennison

##### Active Member
oops, hope it helps someone down the line

#### JakeBlanton

##### Active Member
I thought Great Britain used Imperial measures for a lot of things?
The UK uses metric for certain things and Imperial for others. Their Imperial system is not the same as the US customary system though. For example, an Imperial pint of beer is 20 Imperial oz, but their ounces are slightly smaller than US ounces, so if you convert it to US ounces, you around 19.2152 US oz per Imperial pint. Beer must be sold in pubs in Imperial Ounces, so that is a plus.

35.19508 Imperial Ounces per liter
33.814023 US Ounces per liter

You will find over there that distances between cities on the highway are measured in miles, the distance to an exit that is fairly close is measured in yards, but the clearances of the bridges are measured in meters.

So, when you see a car over there advertised as getting a certain mpg and wonder why the same exact car in the US gets worse gas mileage, you have to remember that their gallons are larger, thus the vehicle can go further on their gallon than it can on the US gallon.

As an engineer, I can use metric, US customary, or even Imperial if necessary. Depending upon what I'm doing, I'll use what is most convenient to use.

I think that some people who have trouble with mold volumes are failing to understand densities of the various ingredients and they might also not know that the US ounce (volume) is not the same as the US ounce (weight) even for water. In the metric system, *originally*, 1 kg *was* defined as 1 liter of water. Currently, it's defined as:

"The kilogram, symbol kg, is the SI unit of mass. It is defined by taking the fixed numerical value of the Planck constant h to be 6.62607015×10−34 when expressed in the unit J⋅s, which is equal to kg⋅m2⋅s−1, where the metre and the second are defined in terms of c and ΔνCs."

https://en.wikipedia.org/wiki/Kilogram#Definition

Not exactly something that you can do in your home lab, but it's within 30 ppm of the original definition, so we can get away with the 1 ml = 1 gram of water approximation.

The difference between dry and liquid measurements in the US can get confusing since many suppliers of products do not necessarily state whether it is a dry or liquid measurement that their product is sold in. Sometimes oils are sold by the liquid gallons and sometimes by pounds.

1 dry gallon = 268.8025 cu-in = 4404.883771 ml
1 fluid gallon = 231 cu-in = 3785.411784 ml

Also, we need to remember that even the rough figure of 1 g = 1 ml of water is assuming that the water is pure and at it's maximum density (approximately 4C). Most other things that go into these soap recipes have their stated densities at a different temperature. For example, soybean oil might be 0.9193 g/ml at 75F, but it is 0.9023 g/ml at 120F and 0.8615 g/ml at 230F.

https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1016&context=chemeng_biomaterials

So, for me at least, I would use the metric system for any sort of recipe where the measurements needed to be critical. That way, you only need to convert the size of your mold from inches to cm (1 inch = 2.54 cm *exactly*). Of course, this is assuming that you have a scale that measures in grams.

oops, hope it helps someone down the line
That is my view also. There are some people who are rather anal-retentive about posting to old threads and think that you should start a new thread. I disagree with this since I find it more convenient for everything to be in one place than possibly in 20 different threads which are often repeating stuff that was in the other threads.

Unlike many people who are on this forum or on the various YouTube channels about soap making, I have no desire to turn it into a commercial endeavor. I'm doing it so that I can get a use out of some of my older used fry oil instead of just mixing it with my dogs' dry dog food (they really like it though). Plus, I want to be able to create a mechanic's soap that is ever better than the Lava brand. Instead of pumice, I'm thinking of using aluminum oxide blast media. No fancy fragrances, just basic soap that will clean grease off my hands after I've been working on something in my workshop.

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#### linne1gi

Supporting Member
I don’t know what aluminum oxide blast media is but I do know that you cannot mix soap with aluminum (the reaction between NaOH and aluminum produces hydrogen gas).

#### JakeBlanton

##### Active Member
I don’t know what aluminum oxide blast media is but I do know that you cannot mix soap with aluminum (the reaction between NaOH and aluminum produces hydrogen gas).
Used in "sand" blasting to remove rust or whatever from the surface of a part. Depending upon what the part is made from, there are various types of media that could be used. For softer metals, you might use ground corn cob or baking soda.

Since this would be mixed in at the end of the hot process cooking, just before pouring into the mold, I would think that there would be little (if any) lye left to react with aluminum. Whether lye will even react with aluminum oxide is probably something that I should test, just for curiosity's sake though.

EDITED:

Doing a quick web search, I came up with this:

https://chemiday.com/en/reaction/3-1-0-208

Looks like as long as you keep the temperature below 900C, you don't have anything to worry about. I'm pretty sure my crock pot won't go that high.

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#### linne1gi

Supporting Member
My concern also is that soap doesn’t mix well with any metals. That’s why we use distilled water, so as not to have any trace metals in the soap. Metals in soap promote DOS. Dreaded orange spots. Obviously it’s your soap, you do what you wish. But I advise against it.

#### shunt2011

##### Moderator Emeritus
Moderator Emeritus
Adding any kind of metal would absolutely enhance the possibility of it going rancid much much quicker. Even metals in tap water can cause it.

##### Member
Hey! I'm new here and have been struggling with this calculation for a long time now! Thank you

#### SpaceCorgi94

##### Well-Known Member
I'm not sure if I somehow missed it (sorry if I did) but is anyone aware of a way of doing this entirely in Metric? (using ml for the mould volume and grams of oil?)

Because all my units here in Metric here in Australia, I've found that trying to constantly go back and forth between converting from Imperial, not only is it difficult, but I've also unfortunately had this calculation work out badly for me during an attempt to make one of my soaps

#### linne1gi

Supporting Member
I'm not sure if I somehow missed it (sorry if I did) but is anyone aware of a way of doing this entirely in Metric? (using ml for the mould volume and grams of oil?)

Because all my units here in Metric here in Australia, I've found that trying to constantly go back and forth between converting from Imperial, not only is it difficult, but I've also unfortunately had this calculation work out badly for me during an attempt to make one of my soaps
I think it’s height times width times depth times .08 for metric. Multiply times .04 for ounces. But I am not positive. Here’s an article I have about it. https://l.facebook.com/l.php?u=http...LMP974-Z1DIMOd5u9bm9wLQB4gLZ4wyA8IB-YxR_r&s=1

#### lshone

I'm not sure if I somehow missed it (sorry if I did) but is anyone aware of a way of doing this entirely in Metric? (using ml for the mould volume and grams of oil?)
Metic volume is measured centimeters. Length x width x height = cm3. (one ml = one cm3) The conversion factor between cm3 and cubic inches (ci) is .578.

If the oil (oz) to volume (ci) ratio is .7 (imperial) then multiply .70 oz/ci * .578 = .40 grams/cm3 (metric).

.7 is the mythical ratio given out by all over the internet. Lye concentration and superfat ratios will change this number. Attached is a table of oil to volume ratio for various lye concentration and superfat values. This should get you pretty close.

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#### Soapydaze

##### Member
Hi everyone.I wanted to post this as a sticky so all could learn how much oils are needed for your mold. Here is the way to figure it.

Lets use a log mold that is 12 inches long, 3-1/2 inches wide, and you want to pour to a depth of 2-1/2 inches.

You take length X width X height of pour, that number X .40. So;

12 X
3.5=
42

42X
2.5=
105

105X
.40=
42 ounces of oils needed for this mold.

Apply these same numbers for your mold size, weather a log, slab, or block.

Paul
Thanks Paul,,,, happy Monday soapmaker

#### Zany_in_CO

##### Saponifier
Hi everyone.I wanted to post this as a sticky so all could learn how much oils are needed for your mold. Here is the way to figure it.
Great information, Paul and I agree, it should be a sticky!

Or you can do what I do. I use Summer Bee Meadows Soap Calc & Recipe Resizer that allows me to enter the dimensions of my mold on the next page after I've done the calculation. This is especially useful for the math-challenged like me.

#### shunt2011

##### Moderator Emeritus
Moderator Emeritus
Great information, Paul and I agree, it should be a sticky!

Or you can do what I do. I use Summer Bee Meadows Soap Calc & Recipe Resizer that allows me to enter the dimensions of my mold on the next page after I've done the calculation. This is especially useful for the math-challenged like me.
He hasn’t been here in 10 years.

#### Steve85569

Supporting Member
Hasn't been here in a long time but the information he left behind helped me - many years ago.

#### Something witty

##### Active Member
P.S. -- one way to figure out the volume of the mold is to fill it all the way with water, then pour the water into a measuring cup. Then, simply multiply the amount of water in the cup with .40 to get the amount of oil to use.
This probably works well for novelty shapes too (inbeds and more). You can weigh it in your preferred measure unit then mark it on the bottom of the mold for future reference.

#### Something witty

##### Active Member
..

Just one question .. when the M&P base is in blocks, how do you know how much to melt to get the "liquid amount"? I hope that makes sense.. for example, say my mould held 100ml of water, how much solid block soap do i need to weigh out in order to have 100ml of melted soap? One would assume around 100g, but i dont know...

That may have a really easy and "commonsense" answer, but times when i've used this method, ie measuring how much water the mould can hold, i've not been totally successful, had a bit too much most of time..

Thanks very much everyone would really appreciate an answer for this
After I use a mold for the first time I take the results and put it back on the scale to get the total weight. Then mark the bottom with a permanent marker for the future.
Hope that helps