# 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. Aug 16, 2013

### DeeAnna

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"...the .4 was hit or miss -i rarely use full water..."

Yep, same here. I am wary of swallowing "common wisdom" without first chewing it well. When I read about the 0.4 rule, I took the time to figure it out for myself. I realized it would overestimate the size of my molds, so I just did the math from scratch to figure the mold sizes I wanted.

On a slab mold, oversizing the depth of the mold is not a big deal. But for a loaf mold, the bar size and shape can get really messed up if the volume calculation is not reasonably accurate.

2. Aug 16, 2013

### sososo

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Don't foget to put in soapcalc: 0%SF and "Lye concentration"=33% - because these are the values I used in my formula. And pay atention to SAP value to be the same as in soapcalc.

Ok, let's see. So now you have 3 oils, not just one. In general, I will use the same demonstration I used for one oil but now we have three oil density - OD1, OD2, OD3, three SAP values - SAP1, SAP2, SAP3, three oil weights - OW1, OW2, OW3, three oil volumes - OV1, OV2, OV3 and thre oil percentages - P1, P2, P3.

LW=OW1*SAP1+OW2*SAP2+OW3*SAP3
WW=LW*(100-33)/33=LW*67/33=(aprox) LW*2=(OW1*SAP1+OW2*SAP2+OW3*SAP3)*2
OV=OW1/OD1+OW2/OD2+OW3/OD3
LV=LW/LD=(OW1*SAP1+OW2*SAP2+OW3*SAP3)/LD
WV=WW/WD=(OW1*SAP1+OW2*SAP2+OW3*SAP3)*2/WD
So,
TV=OV+LV+WV=OW1/OD1+OW2/OD2+OW3/OD3+(OW1*SAP1+OW2*SAP2+OW3*SAP3)/LD+(OW1*SAP1+OW2*SAP2+OW3*SAP3)*2/WD

Now we will write OW2 and OW3 using OW1:
OW2=(OW1*P2)/P1
OW3=(OW1*P3)/P1

So, TV using only OW1 is:
TV=OW1/OD1+(OW1*P2)/P1/OD2+(OW1*P3)/P1/OD3+(OW1*SAP1+(OW1*P2)/P1*SAP2+(OW1*P3)/P1*SAP3)/LD+(OW1*SAP1+(OW1*P2)/P1*SAP2+(OW1*P3)/P1*SAP3)*2/WD

or:
TV=OW1*(1/OD1+P2/P1/OD2+P3/P1/OD3+(SAP1+P2/P1*SAP2+P3/P1*SAP3)/LD+(SAP1+P2/P1*SAP2+P3/P1*SAP3)*2/WD)

so:
OW1=TV/(1/OD1+P2/P1/OD2+P3/P1/OD3+(SAP1+P2/P1*SAP2+P3/P1*SAP3)/LD+(SAP1+P2/P1*SAP2+P3/P1*SAP3)*2/WD)

...and now, that you know OW1, for calculate OW2 and OW3 you have these two:
OW2=(OW1*P2)/P1
OW3=(OW1*P3)/P1

3. Aug 16, 2013

### pahbi

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Thank you Sososo, I achieved success with my spreadsheet.

I created a mold with small blocks that can be adjusted based on the size of the soap loaf to create.

I can now input the measurements of the mold into my spread sheet, and be confident I have accurate calculations. My values compare almost exactly with Soapcalc, with the only differences due to me rounding to the nearest gram.

The next step will be to upload the spread sheet to Google Docs, so that I can access the spreadsheet on my android tablet.

I will need some time to really digest and understand all of the calculations.

Thanks again,
- Paul

4. Aug 17, 2013

### bodhi

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Exactly! Except math isnt my strong suit so i figured, 'hey cant hurt to try it anyway'. Yeah. I was scurrying for molds mid pour. When i actually sat down to figure it out i got as far as the water concentrations and stopped because i couldnt deal with trying to figure the calculations. Now I see why, lol.

And bravo Sososo! Kowtow, kowtow.

5. Aug 19, 2013

### sososo

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Not very complicated. I'm happy that this calculations will help somebody.

6. Aug 19, 2013

### Hazel

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Thanks everyone! I've merged this topic with the sticky "How to figure how much oil for mold" since it is related to the thread and made a permanent redirect to it.

7. Sep 28, 2013

### BrambleNBumble

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Newbie here and I'm still confused on how to figure out how much oil to use for a mold. I bought a three pound mold but all the recipes I'm finding are for five pounds or higher. Is there an easy way to figure this out or is it more trial and error?

8. Sep 28, 2013

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Easiest way I've found is to use the formula in the first post to find the weight of oils for your mold. Then convert the weights of the oils to % of recipe and run that through a lye calculator of choice. Example: For a 3 oil basic bar the posted recipe

Coconut Oil 270 gr
Olive Oil 360 gr
Palm Oil 270 gr

Convert that to % of recipe and you get

Coconut 30%
Olive 40%
Palm 30%

My small mold takes 695 gr of oil so plugging all that into my lye calculator comes out with

Coconut 209 gr
Olive 278 gr
Palm 209 gr

hope that helps.

9. Oct 5, 2013

### gruntedsoaps

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I have never moved so fast for a muffin pan ever in my life. lol. Im new so I tried it blindly. I WAS WAY OFF. were talking it filled my loaf pan and a muffin pan. and they were all filled to the top, the loaf pan actually has a mountain on it. lol. whatever it worked and I got all the soap I could.

10. Oct 27, 2013

### A1will

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Post for future. Reference

11. Nov 6, 2013

### G Str

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I'm not sure if this has been pointed out so far, but the 0.40 thing works only for imperial; inches and ounces.
If you use metric, grams and centimeters you must use about 0.70.

Proof:
say you want to fill a mold with dimensions of 2x3x4 (in inches). The volume is 24 cubic inches. You do the 0.4 thing and get 9.6 oz of oils.
now try that in cm. 1 in = 2.54 cm, so the dimensions of mold will be 5.08x7.62x10.16 in cm. That's a volume of 393.29 cubic centimeters. Do the 0.4 thing and you get a number of 157.32. What's that? Grams? Let's check. 1 oz. = 28.35 grams. 157.32/28.35 = 5.55 oz. You're 4.05 oz. short. Now try it with 0.7. 393.29x0.7 = 275.3, convert to oz. and you get 9.7 oz of oils. Now that's more spot on.
Where I'd get 0.7? From sososo's calculations, the same way he proved the 0.4 thing.

So long story short, it's 0.4 for ounces and inches, 0.7 for grams and centimeters.

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12. Nov 25, 2013

### The Efficacious Gentleman

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Not sure if it's already been covered, but for those that struggle with maths, you can use the formula for calculating how big the mold needs to be depending on the size of your batch -

Let's say I have a 7x5x2 inch mold - that's 7x5x2x0.4 to work out the oz of oils = 28 oz.

But I'm making a new mold (will swap to metric as that is what I'll be working in) and I want to make a 550gm batch 8cm wide, 5cm deep. To work out how long my mold would be is 550/0.7 (for metric!) /5/8 = 19.64cm long. Oils/0.7/height/width.

Now 19.64 is a pain to get and wouldn't give me regular sized soaps, so I can work out the depth I'd get if I made it 20cm long - Oils/0.7/width/length = depth. 550/0.7/8/20 = 4.9cm deep.

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13. Nov 25, 2013

### MoonBath

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:Kitten Love: I'm not a math person at all. So, this is probably a stunningly stupid question, but how does this solve for the space the water takes up?

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14. Dec 1, 2013

### tryanything

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It's magic! Seriously, just go with it. It works. I'm no math person either but I've successfully used this formula for many different mold shapes. Maybe someone else will chime in with a more technical answer.

15. Feb 3, 2014

### brigettevelasquez

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Hi soap makers! Im a new soap maker and new in SMF as well. I have this homemade wood loaf mold and i was able to figure out how much oil to use by weighing the mold and then i press tare on my weighing scale and pour in rice grains inside.

16. Feb 3, 2014

### new12soap

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It doesn't exactly solve for it, but it does take it into account. The volume of water in 1 cubic inch is 0.55 ounces. The same volume of oil will weigh less than that because oil is less dense than water (that's why when you mix oil and water, say in your salad dressing, the oil will float on top). Using 0.4 ounces of oil (by weight which is how we measure when making soap) per cubic inch of mold space, that allows for the addition of water and lye.

Remember, we are converting volume measurements to weight. This is a very simple formula that allows for using FULL water, and then the user can adjust for water discounts or additives.

It does work!

17. Feb 3, 2014

### The Efficacious Gentleman

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Have you done the calculation too, to see if they marry up?

18. Feb 3, 2014

### brigettevelasquez

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Yes i computed using soapcalc. So if my total oil weight is 500g + 35% of water the soap mixture will fit my mold

19. Feb 3, 2014

### The Efficacious Gentleman

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How does that compare with the w x h x l x 0.7 calculation on the mold space?

20. Feb 3, 2014

### brigettevelasquez

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Rice grain weight = 700g

So if your water percentage is 35%

700g * 0.35 = 245g (water weight)

700g - 245g = 455g (oil weight)

haven't tried the formula WxLxH x 0.7 but will try it soon

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