Doubling a soap recipe

by Elizabeth
(New Zealand)

I am sure this subject has been covered but just to satisfy my panic. Can I double this simple cold process Castile soap recipe?

- 1417 grams olive oil
- 425 grams water
- 178 grams lye

I am new to soap making and have made this recipe and it has turned out perfectly.

I really am busting to give it another go but want to make it much bigger as my husband made the mold far too big and instead of slabs I would love to cut it in slices

Also, have I worked it out right that it makes a 2.020kg bar soap by adding all the bits up and that is what dictates the size of mold to use?

Not sure on that bit as I'm useless at maths and the finer details elude me but I am still going to do it.

Thanks for any help you can give me.


Hi Elizabeth!

You most certainly can double the recipe you have listed above. I ran your recipe through Soapcalc to be sure the measurements were correct and to confirm the total batch size before cure.

You are correct that the recipe makes just over 2 kg of soap. Your batch has an 8% superfat and has 30% water by weight of oils if you wanted to put that down in your notes for future reference.

To scale your recipe to fit your soap mold, you can use the following formula. It will determine how much oil you need in your recipe. Make sure to measure your mold in INCHES.

Length of mold x Width of mold x Height you want your soap to be x .40 = ounces of oil needed


One of my soap molds is 6" x 6" and I want my soap to be 2.25" high so the calculation will be:
6" x 6" x 2.25" x .40 = 32.4 ounces

Since you are working in grams, convert the ounces over by multiplying the ounces by 28.375. (There are 28.375 grams in an ounce)

32.4 ounces x 28.375 = 919.35 grams
(I use 900 grams in my recipes for simplicity)

Here is the link to the page where I have the formulas for calculating how much oil you need in a recipe to fill your soap mold. You will need to scroll down to the bottom of the page.

Once you know how much oil you need, go to Soapcalc to find out how much water and lye you need in the recipe.

If you are unsure of how to use Soapcalc, don't worry! Each section of the calculator has a number. Click on the number for an explanation of that section. Using a soap calculator can seem a bit confusing at first but once you have done it a few times, you will find it an invaluable tool you can't live without!

Good Luck and Happy Soaping!

Cathy Winsby

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Thank you
by: Elizabeth

Thank you so much Cathy for doing that for me.

I am going off to the supermarket in the next 2 days. I have to plan my trips as it's a 2 hour drive there and that's why I needed to know if I was on the right track before I went and bought more olive oil for the soap.

I will get my mathematically magical husband to do the workings out now for the mold.

A huge thank you again. Can't wait to have another go.

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