# How to figure how much oil for mold.

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#### DeeAnna

##### Well-Known Member
Here's more background on this topic -- http://www.soapmakingforum.com/showthread.php?t=58581

"...As you all have been sharing in this thread, some soapers will end up with too much batter from using the 0.40 rule, and some won't have enough. So it's obvious the 0.4 rule is simply a rough rule of thumb. Whether the original person originally came up with this number empirically or by calculation, it really doesn't matter anymore. What does matter is the 0.40 rule has been around for some years now and soapers are still using this rule of thumb, so it is proving to be reasonably helpful for most people most of the time, despite its limitations...." --DeeAnna

#### isha

##### Well-Known Member
I use imperial system... Weighing. In grams
So this is what I've learnt and used.. Works well
You need to calculate the size of mould in cms. Instead of inches and multiply by the std multiplier 0. 72
So now calculate (in cms)

VOLUME =L X B X H
Weight of oils = V X 0.72 (GRAMS)

for pvc of round mould. ( IN CMS)
V= pi X R X R X H

Weight of oils (grams) = V X 0.72

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#### Garnet_Tree

##### New Member
Ounces of Oils

These formulas work for OUNCES of oils.

If you want to work in grams then you need to do the calculations and then convert to grams. Many soap calculators do this for us. There are approximately 28.35 grams in 1 ounce.

To make the conversion, multiply length (in inches) x width x height x .4 x 28.35 to get the grams of oil needed.

#### isha

##### Well-Known Member
@ garnet tree.. I've mentioned a simpler version of this. Hope it helps [emoji4]

#### SaltedFig

Lifetime Supporter
I think mzz said it most clearly in 2012, with this:

For metric I use:
Volume (cm3) x 0.7 = ? g oils
So,
Imperial, use 0.4
Metric, use 0.7

Like all general rules, this one needs to be adjusted for your personal recipe.

For anyone who would like to avoid doing volume math, this link is to a straightforward volume calculator for cubic and cylindrical molds (just plug in your measurements in imperial or metric, and it will give you the volume): http://www.ifocas.org/calculator.htm

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#### isha

##### Well-Known Member
Thanks saltfig.. That went on my bookmark immediately.. U saved a ton of brain scratching time for me

#### rjuconnfan

##### Well-Known Member
Good info..exactly what I needed to know for my first soap. I have no idea how many molds to have ready to go when I start mixing.....I don't want to be running all over trying to find things. I only have a couple small loaf style to start but will make up a few from recycled milk containers etc. Just in case! Thanks for the post.

#### AnnaBanana

##### New Member
12 pages!
So I’m new to soaping. Only made one batch so far. Got myself off kilter using the measurements of the mold, cubed x .40, because I was a bit befuddled where the lye water fits into that calculation. Using the calculations I got the oz of oils for a 3.5 lb. After adding in the lye water, I now had almost 5 lbs of soap not 3.5 lbs. Luckily I had a small plastic tub for the extra. How does the lye water factor into the calculation. That water takes up volume too.

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#### DeeAnna

##### Well-Known Member
Yes, you are right -- the lye solution takes up space too. The 0.40 estimate allows room for the water part as well as the oil part, so you don't have to deal with the lye solution volume.

Remember, however, that the 0.40 estimate is an estimate, not a surefire number that works exactly right all the time. The 0.40 number is based on assumptions about the proportions of water, NaOH, and fat that make up a typical batch of soap. The actual volume of YOUR soap may be different depending on how you design your recipe. Do you use more water than is typical? Did you include bulky additives? How much fragrance did you use? Etc. (See also Post 229 in this thread.)

Some people use 0.38 instead of 0.40 to estimate the recipe size for their mold, because they find the 0.40 number overestimates the volume of soap they need. Others might use 0.42.

Now that you know how much extra soap you made, you can tweak the amount of fats for your recipe until the batch fits your mold without any excess, if that's what you want to do. Some people like to make a little extra batter, so they can fill a few guest-sized soap molds as well as fill their main mold.

#### John Harris

##### Well-Known 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. :wink:

Paul
Does this work using centimeters?

#### DeeAnna

##### Well-Known Member
Does this work using centimeters?
No. The 0.40 factor is for inches and weight ounces. Use 0.70 for centimeters and grams. You're on your own if you use any other combination of units.

I show the math to derive both rules (0.40 and 0.70) in this article -- https://classicbells.com/soap/moldBatchSize.asp

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#### Kosmerta

##### Well-Known 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. :wink:

Paul
If only I had seen this post 12 hours sooner. I measured my mold in cm, calculated ml from there and converted ml to oz. My batch was allllmost perfect for my mold, but I had about 2.5 oz of extra batter. I had to rush an find my 4 oz cube mold from my supply area for the excess!

#### KDP

##### Well-Known Member
Thank you for this, Paul! My son asked what I wanted for Christmas....please build me a slab mold..I've been researching for directions/instructions. This is perfect! Thanks!

#### LaPrairieLady

##### Member
I put the water in a measuring cup and count the ounces until my mold is full. I know that 1 pound of soap is 16 ounces oil + 6 ounces water + 2.23 ounces lye give exactly 3 cups of batter (24 ounces) I mix in my pyrex 4 cups.

#### lshone

Lifetime Supporter
No. The 0.40 factor is for inches and weight ounces. Use 0.70 for centimeters and grams. You're on your own if you use any other combination of units.

I show the math to derive both rules (0.40 and 0.70) in this article -- https://classicbells.com/soap/moldBatchSize.asp
I setup a spreadsheet to work out the volume of oil based on the ClassicBells link. My original goal was to create a 4oz bar, so this spreadsheet kinda evolved from that. I use loaf molds so the spreadsheet is setup for any type of L x W x H volume calc.

I've reworked the example from the ClassicBells link provided, but set the superfat and FO values to zero. When I use a 33% lye conc. I get a .7 conversion factor almost exactly.

I've added the conversion factor to the spreadsheet so I can see how it changes with the lye concentration. It's more out of curiosity now, as the spreadsheet calculates what I need. I let the spreadsheet do the work, then I run everything through soapcalc or soapmakingfriend to get a nice print out of the recipe.

Here is a link to the spreadsheet I use ==> CP Soap Resizer

The cells with the orange border are where I "input" data that needs to be changed, based on whatever formula I'm using and whatever mold size I'm working with. This spreadsheet works with lye concentrations between 20 and 50. The "blue" cell gets its value from the lookup table in sheet2, based on input % lye concentration.

I got the lye density values here ==> Handymath.com
The oil densities I just found on the internet. 99% of the time a value of .92 is close enough.

#### Kosmerta

##### Well-Known Member
I'm still slightly confused about the 0.4 rule. This post says AreaX0.4= weight of oils. Does this mean total weight of batter of JUST the oils? Once my lye water is added my batter would be a larger volume than just the oils clculated by the 0.4 rule.

Is the rule already claculated to include lye solution? If so, what concentration? I like to make my lye at 33% using 2:1 water: NaOH.

#### DeeAnna

##### Well-Known Member
"...This post says AreaX0.4= weight of oils...."

It's VOLUME X 0.4 = weight of oils.

"...Does this mean total weight of batter of JUST the oils?..."

The answer you get from the 0.4 Rule for inches and ounces (or the 0.7 Rule for centimeters and grams) is just the weight of oils.

"...Is the rule already claculated to include lye solution? If so, what concentration? I like to make my lye at 33% using 2:1 water: NaOH...."

The number 0.4 is there to account for the volume of the water and NaOH. It's based on the assumption of using a 28% lye concentration. It's also based on assumptions about the particular fats in the batch. It's not just the lye concentration that affects the batch volume.

If you use a higher lye concentration, that will reduce the volume of batter slightly. If you use more coconut oil or other fats with high saponification values, the volume of batter will be slightly less. If your batch includes fragrance or any other additives, the batch volume will be slightly higher.

This Rule is a quick and easy way to estimate how bit of a batch to make when using a new mold for the first time. It's not ever going to be perfectly accurate for all soap recipes all of the time. I know a more complicated method could be created to nail down the answer within a narrower margin of error, but honestly most soap makers are really looking for quick answers that require minimal math and measuring. That's what this Rule accomplishes.

I discuss the assumptions used in the 0.4 Rule in my article here: https://classicbells.com/soap/moldBatchSize.asp

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#### Brokinkiy

##### New Member
I just got a small mold for sample bars and this is just what I needed. I wish I had looked at it before I made my large batches. Great info, Thanks Paul!

#### Masterok

##### New Member
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?

#### DeeAnna

##### Well-Known Member
"...That might be a percentage of volume. So in a typical recipe of soap is 40 percent of the volume from oils?..."

@Masterok -- Good thought, but not really on-target. See the last paragraph in my last post #237 for a link that answers your question.