How to figure how much oil for mold.

[bodhi]

"...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.

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.

 

[sososo]

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

 

[Hazel]

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.

 

[BrambleNBumble]

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?

 

[alaskazimm]

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.

 

[gruntedsoaps]

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.

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.

 

[A1will]

Post for future. Reference

 

[G Str]

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.

 

[The Efficacious Gentleman]

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.

 

[MoonBath]

:wtf: 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?

 

[tryanything]

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.

 

[brigettevelasquez]

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.

 

[new12soap]

:wtf: 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?

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!

 

[The Efficacious Gentleman]

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.View attachment 5727

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

 

[brigettevelasquez]

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

 

[The Efficacious Gentleman]

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

 

[brigettevelasquez]

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

 

[The Efficacious Gentleman]

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

Please do! I'm interested to find out more about your measurements................... :grin:

 

[brigettevelasquez]

I use this same method in making silicon mold so i can figure out how much silicon rubber to use for my mold. And i tried it on my first batch of soap and it worked!

 

[Saponista]

Wxlxh x0.7 worked like a dream for me