Using a Soap Calculator

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Using a soap calculator is an essential part of soap making of any sort - with the exception of melt and pour, of course.

So, a few days ago, I started making my first batch of laundry soap. Now, I have really researched this as I had a couple of concerns about the lack of detergent and the effects this can have on your clothes, but I think I have managed to get my final recipe right. Only time will tell, I guess. I will include my findings, and any changes I make, in post three so that you can make an educated choice about whether or not you want to use this soap powder recipe. Even if you decide against it, it makes an amazing stain removal bar on its own.

I had everything I needed at home (one of the bonuses of doing what I do for a living) so it was fairly easy to get the first stage done.

If you decide to try this recipe, it is important to understand that you are working with chemicals. You need to wear the correct safety equipment. Even wearing all of mine, I managed to get a small chemical burn on my wrist.

Today we are looking at the laundry soap recipe design and learning how to approach any soap tutorial you find on the internet. Once we understand the soap calculator, we can then move on to making the bar soap and finally making the soap powder itself in parts two and three.

I used coconut oil to make the bar soap, with a 0% super fat, but you can also use lard if you want to save even more money and don't mind using animal fats. It is important that you run this recipe (and any other soap recipe you take from the internet) through a soap calculator. I use SoapCalc. It looks pretty scary, but I'll go through it with you and you'll realise it's actually quite straight forward.

This is an extremely cleansing soap so it is not suitable for use on your skin.

What you'll need:

  • A large plastic spoon,
  • Heatproof non-metallic bowl,
  • Jug,
  • Scales,
  • Safety glasses,
  • A dust mask,
  • Gloves,
  • Stick blender,

Also, be sure to wear long sleeves in case of any splashes.


This is what I used to make my batch of laundry soap, but you will need to double-check with the soap calculator. 

  • 907g Coconut Oil (this is what my one-litre tub weighed in at)
  • 166g Sodium Hydroxide (Caustic Soda or Lye)
  • 345g Distilled Water (you should always avoid using tap water when making soaps as it is not pure enough).

Checking the figures:

It is so important that you double-check any soap recipe you find online (yes I am repeating myself, but you cannot be too careful when making soap). There may be a typo, or the person, no matter how well-intentioned may not actually understand the dangers associated with the making process. So we are going to start there. Open up SoapCalc by clicking here.

Soap Calc Screen

Right, so this actually helps you to make a smaller batch if you want to, although I don't recommend using less than 500g in oil.

Have a good look and familiarise yourself with it. For this recipe, we only need to add a small amount of information.

  • Go to section 2 and change the weight of oils to your preferred unit, I used grams. Then add the total weight of your oils. For me, that's 907g, which is what my litre of coconut oil weighed in at.
  • Next, in section 4 change the superfat percentage to 0. (Superfat is the percentage of fat that is left over after the saponification process. As this is laundry soap, we do not want any fat to remain in the bar. Once you are familiar with working with sodium hydroxide, you may prefer to make this a lye heavy recipe.
  • In section 6 choose your oil from the list. In this case, it should be Coconut Oil 76 deg (the melting point of the coconut oil), unless you are using lard or coconut oil with a higher melting point. Click on add and put 100 in the % bar next to it.
Like this:

 Soap Recipe Washing Powder - Soap Calc example


  •  Then go to section 7 and click on Calculate Recipe and then View or Print Recipe.

You will have this:

Soap Calc Print View Washing Powder 

 What it all means:

Ok, this is the bit you need to pay attention to - if you just skim the whole article, that's fine - but please read this bit with extra care and attention. This is your recipe. This document tells you everything you need to know about your laundry soap - including that you shouldn't use it on your skin!

We will start at the top and we will only look at the parts that are important to this laundry soap project. We will come back to other parts in later projects to avoid information overload.

So, first is to double-check your weights and measures. The recipe is in grams which is what I want, so that is good. The weight of the oil is correct too as is the superfat value as it is at zero. You will notice that you have conversions for the weights to pounds and ounces as well as the grams, so you can work with different scales if you need to.

When we are making soap, we always work with weight. We never work with volume as it is unreliable and nowhere near as precise as we need it to be.

We can see from the recipe that we need to use 344.66g of water. I always round this measurement up to the nearest gram. So 345g of distilled water. We also need 166.20g of lye which I always round down to the nearest gram. Of course, if your scales are precise enough there is no need for rounding. Ignore the fragrance section as we will be adding that to the powder instead of the soap to avoid any adverse effects on the soap making process.

Soap Bar Quality:

Ok, we are only going to look at the figures here. We will briefly cover what they mean, but we can go into more detail when we use soap calculator to make body soap in the future.

Hardness - The hardness of a good body bar is between 29 and 54 according to Soap Calc. As you can see the hardness of this bar is significantly higher than recommended. This will mean that early cutting and grating of the bar will be required when we make the actual soap.

Cleansing - Cleansing should be between 12 and 22. A soap that is too cleansing can dry and even burn the skin. This is one of the reasons that you should not under any circumstances use this soap on your body.

Conditioning - This should be between 44 and 69 for a good body soap but is actually at 10 for this recipe - another good reason for not using it on your skin.

Bubbly - is very high, but we will tackle this when we make the powder itself.

As you can see from the figures, everything is well out of the range of skincare. This is a very strong soap, it is perfect for use as a stain remover for clothes or as part of homemade washing powder. It is definitely not good for your skin. You will also need to ensure that it is kept out of the way of children.

So, that's part one done. Part two should be available next week shortly followed by part three. If you have any questions, please pop them in the comments below and I will do my best to respond to them for you. I am off to do a rebatch now - which I will cover in the future - and turn it into soap powder.

If you find this whole process just too daunting, I have good news. The bars of soap will be available from the website during August so that you can still make your own powder if you would like.

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The information above is not intended to replace medical advice. The use of any information provided by The Druid’s Kitchen is solely the user’s responsibility. The Druid’s Kitchen advises that you consult a health professional before using essential oils or herbs. It is assumed that you will conduct your own research about any skincare or household products made using The Druid's Kitchen's recipes. We can only advise on ingredients and procedures. We do not take any responsibility if you decide to follow any of the tutorials without following safety advice or conducting your own research.

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