# How to figure how much oil for mold.

Discussion in 'Lye-Based Soap Forum' started by Soapmaker Man, Mar 26, 2008.

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1. Oct 17, 2011

### SudsyKat

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Just tried this calculation over the weekend - I had a new large mold and wasn't sure how much soap to make. Anyhow, it was kind of close, but did not make enough soap to fill my log mold to the desired height. I even added 4 oz of oils just for good measure (it's a 22 inch log mold). I think the difference is in the amount of water (or lye concentration) you use. I was using a fairly low water amount (33% lye concentration). I know people frequently use more water than that, so I'll have to take that into account next time. Is 38% pretty much the standard (I saw someone else on this post mention it)? I've used all different amounts, depending on the recipe. To the original poster - thanks for posting this. It was helpful to get a general idea of the amount.

2. Oct 21, 2011

### BBrandDesign

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Wooden soap molds are no longer the only option out there to use for soap making. In all honesty, you can pretty much use not anything as long as it does leak, and does not react with the soap and you can get the soap out of it later.

3. Nov 7, 2011

### tlm884

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I recently found out why you multiply the volume of the mold by .4. The .4 is actually the percent of Water as a % of oil. It looks like the formula here uses 40% instead of the standard 38%.

So, if you are using 38% you would multiply the volume of the mold (width X height X length) in cubic inches by .38. This will give you the amount of oil the mold will hold when 38% water is used.

So, if you are using a different amount of water, the mold will hold a different amount of oils. However, the mold will always same the same volume of soap.

4. Nov 7, 2011

### chibilightangel

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The best mold size calculation come from TheDish soap forum. It's a metric calculation but so far has proven as most accurate for me as I can change my water and know by how much I should adjust the recipe.

Metric calculator found here: http://www.thedishforum.com/forum/index.php?showtopic=149087&st=0&p=2629990&#entry2629990

conversion factors: 28.35g per oz (weight)
2.54 cm per inch

Works for any size mold provided you can calculate the volume.

5. Dec 21, 2011

### Iris Reola

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I'm going to attempt this in reverse to find the final dimension for a mold needed to fit 35 ounces of oil so that my father can build me a mold to suit my needs. I'll let you guys know how that works out and whether or not I completely suck at algebra. 8D

6. Mar 18, 2012

### Robbiegirl

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Where does the .40 come from ? That might be a percentage of volume. So in a typical recipe of soap is 40 percent of the volume from oils?

7. Apr 15, 2012

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8. Jun 9, 2012

### soxysarah

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dose this work with cupcake moulds ?

9. Sep 1, 2012

### danahuff

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Well, I know this is an older thread now, and maybe no one cares, but l*w*h is the formula for the volume of a rectangular prism. A soap recipe is comprised of more than just the oils, hence multiplying it by 0.4. I imagine that at some point, someone calculated that unsaponified oils totaled about 40% or 0.4 of the total volume of the batch when it's at trace. However, that person is way smarter than me. I kept making too much soap for my mold until I happened on this formula somewhere else. I was trying to total the volume of liquids—oils + lye—and it wasn't returning the right results.

10. Nov 12, 2012

### shafaq007

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When we multiply the LxWxH are we measuring in inches or centimeters. I have seen a similar formula except it says to multiple the result by .38.

11. Nov 12, 2012

### Relle

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Example

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.

Work it out in inches and then convert the volume if you want metric. 42 ounces is 1190.7 grms.

12. Nov 13, 2012

### mzz

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For metric I use:
Volume (cm3) x 0.7 = ? g oils

13. Dec 13, 2012

### jkoehn

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Thank you sooo much!

14. Dec 28, 2012

### soapbuddy

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I go by length X height X width, then multiply all by 0.37 That seems to give me the most accurate measure.

15. Feb 2, 2013

### Cherry Bomb

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Math Enthusiast

SoapMaker Man, thank you so much for posting this formula! I love chemistry and I love math! Working your EO quantities needed out on paper will help me feel like I have accomplished something magical! Lol I had planned on using the following link to figure out my EO quantities but your way seems like more fun! Just call me insane in the membrane!

http://www.brambleberry.com/Pages/Fragrance-Calculator.aspx

This link is also a good way to figure out your lye %. Once you calculate your lye % this link will also give you your total weight and you can use that to plug into the fragrance calculator or use your method!

http://www.brambleberry.com/Pages/Lye-Calculator.aspx

Anyways, I am new to this and from a newbie....this was great information! Thanks again and have a "Soap"tacular day!!!!

16. May 1, 2013

### souljasam

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so i was trying to do this to figure out how much i needed for my 13" x 3.5" x 2.5" mold in order to make a 4 pounds of soap like the mold should hold.

2.5
3.5=
8.75

8.75
13=
113.75

113.75
.40=
45.5oz of oil

now when i put that into the lye calculator on soapcalc.net it says i need 17.29 oz water and 5.856oz lye. now

45.5+17.29+5.856=68.646 about 4.5 oz more than 2lbs(64oz)

what am i doing wrong? ive even tried it with .38 to get 43.335oz of oil to get an end total of 65.214oz. closer but still over an oz off.

17. May 1, 2013

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The cured Soap will lose around 4.5 oz of water due to evaporation.
You'll be fine

18. May 1, 2013

### souljasam

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ahhh, ok. i figured some evaporation would occur but wasn't sure how much. thanks a lot.

19. Jun 11, 2013

### becca757

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how much oil to use....

Soapmaker....does your method include the water and the lye? I'm fairly new to making cp soaps and I'm having trouble with calculating the volume of my mold.
I have a wood mold that is 7 in long, 3.5 in wide and 2.75 in high. Now from my research I was told to multiply the length x width x height which I have and got 67.3. Then was told to multiply that by 0.554 to get 37.2 and then multiply that by 0.9 for a total of 33.5 ounces. I've done that and for some reason when I go to fill my mold I end up filling my mold to the top and still have more soap left over. Would you mind terribly giving me some advice on how to correct that? Thank you so much in advance!!

20. Jul 16, 2013

### Bann51

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No. It doesn't include the lye. It tells you the oils. Because I'm new to cp. I started with small wooden boxes I got from the craft store. I did the measurement and came up with my oils. After doing the calculations for them, they called for a 24 oz recipe. I use that for my soap recipe and it fit perfectly into my boxes. So if you do your calculation of 7 x 3.5 x 2.75 you get 67.375 then multiply that by .40, you get 26.95 So your soap recipe should be 27 ounces in oils. Of couse once you run it through a lye calculator, you'll get the water and lye. This is the way I've seen it done on several websites.

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