# Rule of Thumb for Mold Size with Water Discount

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#### BrewerGeorge

##### Well-Known Member
We've all heard the formula of L x W x D x 0.4 to estimate the amount of starting oils a mold will hold.

But I've never seen the derivation of that explained enough to be able to manipulate it for changes. I'm assuming (?) that formula is geared toward a typical beginner 38% water as % of oils setup, so using a water discount should change that formula. I would expect to be able to use more oils in a given mold because there's less water in the finished product.

I usually soap at a 30% lye concentration, and I'm looking to buy some new molds. Can somebody help me with the calculations? I'm finding most of the typical loaf molds too small to hold my typical 40 oz of oil - which I'd like to keep static if possible for several reasons.

#### lenarenee

Supporting Member
Looking forward to seeing where this discussion goes. I gave up using that formula because it never worked well for me.

#### toxikon

Supporting Member
I just fiddle with SoapCalc amounts until the lye water and oils add up to the capacity of my mold. It just means a lot of tweaking numbers then looking at the resulting amount. It ends up working pretty accurately for me.

#### BrewerGeorge

##### Well-Known Member
Looking forward to seeing where this discussion goes. I gave up using that formula because it never worked well for me.
See, I've never really used it either. I sized and built my mold for 40 oz of oils using that formula 18 months ago - and it works - but I've never used another mold. Now I want to replace that with something that has a silicone liner so I don't have to mess with the freezer paper any more, and I don't know what I'm doing.

#### Susie

Supporting Member

#### Gerry

##### Well-Known Member
This is where every country on earth except the USA rules! Hahaha

It's so darn easy in metric. 1 gram of water is exactly 1 cubic cm. Just subtract the water in grams that you would otherwise be using, and thus subtract the cm3 from your volume. No friggin idea on how to do this in the old system, but just convert I guess. Personally I'm too lazy and will keep with the metric.

I keep notes with a sharpy on my wooden molds. I have a nearly full amount of oil listed @ 30% lye, and a 3/4 amount of oil so that I have room to scalp the tops or add imbeds. You never want to fill them even to the top because you'll need to cover to prevent ash and the saran wrap might touch the soap and ruin your design. In the end, it's a bit of trial and error because the volume you fill will depend on what you're doing on top anyway.

#### The Efficacious Gentleman

I'm not sure that the water, while it does have a 1:1 ratio of weight to volume, that it would translate that way in the batter. Salt, for example, does not seem to increase the volume of batter by the volume of salt. It increases it, but not by so much. Would be interesting to see, though

#### lenarenee

Supporting Member
I'm allergic to math. Honestly, I'm trying to find a math tutor I can afford so I can learn basic math (but \$40 a hour??). I like to become certified by HSCG.

I used that standard formula when I fit got my T&S mold. Usually I use a 33% solution. I had exactly enough batter leftover to fill a crafter's choice 1lb mold. Hmm. Must have done the math wrong, right? 2nd time: same result. Okay, repeated mistake. 3rd time...same result. (forgot who...but someone on the forum verified my work)

So I don't use the formula....unless I want to test a 1 ounce sample of fragrance! I've had much better luck with measuring volume (how many cups of water my mold holds), and compare it with a recipe with a known volume. All of my molds have volume amounts Sharpied on the sides.

Wouldn't this show that solution percentage is key? If not, then the amount of oils held the American Soap Supplies tall and skinny is listed incorrectly on their website - that's the only other reason I can think of.

#### BattleGnome

##### Well-Known Member
I always estimate and have a mold or two on hand for overflow.

2# mold = 36oz
My "recipe" uses 25oz (somehow that's the amount of oil I end up with, I don't actually have a recipe yet) and averages around 9oz water on soap calc then I add 1-2oz Fo (plus whatever the NaOH calculates to and my colors). 90% of the time this is good enough for my 8" crafters choice molds. I tend to only have extra when I want shorter bars.

#### BrewerGeorge

##### Well-Known Member
Ok, let's ignore the calculation and just talk experience.

How much soap, by weight of oils, can you folks get into a Crafter's Choice 1501 (8")? How about Brambleberry's 10" similar one?

#### suburbanrancher

##### Member
Just used that mold last weekend and the amount of oils I used did not fill the mold and I ended up with stumpy bars.

According to my soapee recipe, I used 992 grams of oils (35oz) and 33% lye concentration.

I checked the box that says "adjust oil in water amounts."

I made another batch with the Brambleberry 9-bar mold and did NOT check that box and the soap fit up to the very lip.

I'm going to make another batch using the CC 1501 mold and NOT check that "adjust" box and see where that leaves me. I'd rather have too much soap than not enough.

#### penelopejane

##### Well-Known Member
I want to use 1000g of oil each time because it makes it easy.
I have noticed that each batch is a tiny bit different (didn't think of it before but it could be the water content) and I have 2 different molds.
I just have a small 6xbar mold handy to cope with any excess.
Not scientific but saves a lot of stress.

#### mx6inpenn

##### Well-Known Member
I used my new t&s for the first time the other night. I used the formula, 30% water. I had enough soap leftover to fill a 2x3x1 cavity mold halfway, so approximately 2oz. If I had wanted to pile up the top, I wouldn't have had enough, but for what I had planned, it worked perfectly.

*However* it doesn't always work out that way for me. As those in the swap will see, using the formula did not work when I made my soap for that and the bars are a bit stumpy.

#### HowieRoll

##### Well-Known Member
Today an email came out from WSP with a recipe for Pureed Carrot Cold Process Soap. I notice it was sized to use the Crafters Choice 1501 8" loaf mold, and remembered this thread (I do not own this mold). From the recipe they provided, it looks like the mold holds 32oz of oils based on a 33.333% lye concentration and 5% SF.

Also on the WSP page for that mold is a tab with Recipes & Videos relating to that mold specifically. It looks like the recipe for the Apple Crisp CP Soap uses a different lye concentration (around 27.163%, or using 38% water as percent of oil weight, if I've input the numbers correctly) and only 28oz of oils. I haven't checked the other recipes to see variations, but they might offer clues as to how water content will affect amount of oils needed.

...at least I think?

#### suburbanrancher

##### Member
Ok, let's ignore the calculation and just talk experience.

How much soap, by weight of oils, can you folks get into a Crafter's Choice 1501 (8")? How about Brambleberry's 10" similar one?
Made a batch today, the weight of the soap batter in the CC 1501 mold (to the LIP!) was 1854 grams. This was a 44oz oil recipe which, per soapee.com, had a PROJECTED total batch weight of 1804g (63oz). This is with 33% lye concentration, 6% SF and 4% fragrance oils.

The ACTUAL batch weight was 2,054 grams. So, clearly there may be a scale error (everything was measured to the ones place and nothing was over). The one teaspoon used for the oxide and the 3 teaspoons of water for TD do not make an extra 200g of soap.

My take away from this is that for the next attempt, I will use 38oz of oils, and using MY scale I should hopefully end up with a recipe that will fill the mold adequately without overflow. But I think a few trial and error sessions like this will be key to figuring out what works for the scale and mold you have.

#### lenarenee

Supporting Member
I used my new t&s for the first time the other night. I used the formula, 30% water. I had enough soap leftover to fill a 2x3x1 cavity mold halfway, so approximately 2oz. If I had wanted to pile up the top, I wouldn't have had enough, but for what I had planned, it worked perfectly.

*However* it doesn't always work out that way for me. As those in the swap will see, using the formula did not work when I made my soap for that and the bars are a bit stumpy.
Curious; which tall and skinny mold do you have? (different company=different volume)

#### mx6inpenn

##### Well-Known Member
Curious; which tall and skinny mold do you have? (different company=different volume)
Actually, I have no idea. I got it on one of the destash groups. There aren't any markings. 12x2.25x3.25