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April 2, 2018
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April 21, 2018

How to use Soap Lye Calculator

My Soap Calc create a recipe

Let me start this post with a proverb. “Give a man a fish and you feed him for a day. Teach a man to fish and you feed him for a lifetime.” Today, i’ll teach you on how to use My Soap Calc™ soap lye calculator so you can make your own recipes and craft your handmade soap in no time. It’s my birthday and the soap lye calculator that I developed is my gift to my soap making family for their love and support and my little share to the soap making community.  This is also to pay forward all the blessings and gifts I receive everyday. 

soap lye calculator


If you just want to make a quick soap recipe, the most important thing to do is to directly go to Section five, oil section. Then select your oil of choice by weight or percentage. Then click Calculate Now. It’s that easy! 

But if you want to really tweak and play around with your recipes, follow the steps provided below and/or watch the video tutorials:


1. Select Unit of measurement in section one. This unit will be used in the calculations in the soap recipe print-outs. Set at Grams, g by default.

  • Grams, g
  • Ounces, oz
  • Kilograms, kg
  • Pounds, lbs

2. Calculate how much does your soap mold can hold using the Mold Capacity in Section two. This is optional and the calculator would still work even if you leave this blank. There are two selection buttons:

  • Loaf/Slab
  • Cylinder

Next, input the dimensions of the mold in centimeters, cm. Capacity will be automatically calculated and shown for your reference.  

Did you know? That when you calculate the mold capacity, My Soap Calc™ will also help to estimate how much oil do you need to weigh, so you could make just enough soap to fit your mold (This value is shown in Section five, oil section). Yes, this is the first soap lye calculator with mold capacity function. 

3. In Lye section, input your preferred superfat/lye discount. Default value is set at 5%.

Did you know? That My Soap Calc™ soap lye calculator is the only soap lye calculator that accounts for Superfat/Lye discount factor in generating the Soap Quality. You will see the difference in the soap quality when you increase and decrease the superfat/lye discount value. Again, the first one there is.

Select the type of soap you would like to make.

  • Bar soap using NaOH
  • Liquid soap using KOH
  • Dual Lye soap aka Hybrid soap using NaOH and KOH (ratio depends on your preference, default settings 95% NaOH and 5% KOH)

Did you know? That dual lye soap is good for making shaving soaps? You better add that in your soap making bucket list.

Then, input the actual purity of your Lye, you can refer to the Certificate of Analysis (COA) or the product label. Default purity is set at 100%.

Did you know? That the purity of your lye affects your soap. When you buy from Supplier A with 96% Lye and Supplier B with 100% Lye, its performance will be different in your soap. To eliminate this variations, My Soap Calc™ incorporated the purity factor in all calculations. This is the only soap lye calculator that accounts for the purity of your lye whether you use NaOH or KOH in your recipe.

4. Input the Water amount shown as Lye concentration for your recipe. Default value is set at 27% Lye concentration (Full Water).  This is equivalent to ~38% Water as % of oils or 1:2.7 Lye: Water ratio. 

Want to do a water discount? You can either change the concentration to higher Lye concentration (example 37% Lye Concentration for Water discounting if you already know how much is the exact Lye concentration you would like to work with or you can just input discount percentage in Water discount tab (25% in Water discount tab would reduced the original full water weight to 25%, if your recipe originally needs 100g water, it will now show 75g water due to 25% water discount).

My Soap Calc™ is the only soap calculator where you can also input how much part of the liquid you would like to substitute. You can replace it with milk, tea, etc and no need to do manual calculations anymore. Just plug in the percentage and the soap lye calculator will do the job for you. Remember to input the Substitution ID. This ID will be used in the print-out (optional but really cool to have).

5. In the Oil section, input the weight of oils that you need in your recipe. Default value depends on the unit of measure you selected in section 1:

  • 500 g
  • 16 oz
  • 1 lb
  • 1 kg

You can also manually change the weight of oil based on your requirements.

The mold capacity in section 2 helped to estimate how much oils do you need. Let’s say – based on your mold you will need 346 grams of oil, you can then input 350 in the weight of oils to prepare just enough or add more or less depending on your soap making plan.

Another feature added is to show how much total oils by weight and percentage you already added in your recipe so you can choose to add more or reduce the weight or percentage of the selected oils in your recipe and make quick decisions.  There are 150 oils at the moment so just choose the oils at your heart’s content.

6. Fragrance is set at 3% default. You can change this according to your preference. Remember to add the Fragrance ID so it would reflect on the soap recipe print-out (optional but really cool to see it in print).

7. Click Calculate Now to generate the soap recipe summary or click Reset to start over.

Let us discuss the Soap Recipe Summary in another day.  In the meantime, you can Click here to go to the Soap Lye Calculator  and start creating tons of recipes or shop Lye below. Have fun!

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