Soap Lye Calculator (For Liquid and Bar Soap)
Use this lye calculator to quickly determine how much lye, water, and optional glycerin to use in your soap recipes. It works for both bar soap and liquid soap and is based on the same approach I’ve used for years when developing my own recipes. You can adjust settings like superfat, KOH purity, and liquid ratios to match your exact formula.
Lye calculator for soap
Soap type
Oils and fats
Soap settings
Results
Soap qualities
Working with lye requires basic safety precautions, so be sure to use proper protective gear and follow a reliable soapmaking method.
How to use this calculator
- Choose whether you want to work in grams or ounces using the buttons at the top.
- Select the type of soap you want to make. Make sure you’re using the correct type of lye: sodium hydroxide (NaOH) for bar soap and potassium hydroxide (KOH) for liquid soap.
- Enter the oils or fats you want to use. You can add additional oils as needed.
- Adjust the superfat level to your preference. For liquid soap, you can also adjust the KOH purity, liquid ratio, and glycerin amount if needed.
- The calculator will update automatically as you make changes.
- When you’re done, you can copy the results or print them out.
About the soap qualities section
These soap qualities are meant as a quick visual guide for bar soap. They’re based on the fatty acid profile of the oils you choose, which affects things like cleansing, conditioning, lather, and hardness. I’ve kept this simple on purpose so you can quickly compare recipes without getting into the more confusing numbers some soap calculators use.
You’ll only see this section for bar soap, since liquid soap behaves differently and those values don’t translate in the same way.
A couple of quick notes
- Most liquid soap recipes are made with 0% superfat, while bar soaps are often made with around 5%. You can adjust this depending on your preferences.
- KOH purity matters. If your potassium hydroxide is closer to 90% instead of 95%, lowering the purity setting will give more accurate results.
- For liquid soap, glycerin is optional, but it can help speed up the process and make the paste easier to work with.
- This calculator currently includes the oils and fats I use most often in my recipes. I plan to add more over time.
Why I made this lye calculator
For years, I used the Summer Bee Meadow lye calculator to make my liquid soap. I liked how it handled glycerin and liquid soap recipes, and I got used to working that way when I was first learning.
When their calculator became unavailable, I realized how much I relied on it. It wasn’t only about the results. It also handled things like KOH purity and glycerin in a way that worked well for how I make liquid soap, and not all calculators do that.
I even tried to contact them to see if there was a way to keep using it or host it on my site with credit, but I wasn’t able to get a response.
So in the end, I decided to build my own.
One of the things I always appreciated about their calculator was how it accounted for potassium hydroxide (KOH) purity. Many calculators assume KOH is 100% pure, but in reality, most KOH used for soapmaking is closer to 90–95%. From my experience, the Summer Bee Meadow calculator seemed to give results consistent with around 95% purity, which is what I had been formulating my recipes around.
This calculator is designed to give results similar to what I used in my original recipes, while also letting you adjust things like KOH purity, liquid ratios, and glycerin amounts for liquid soap. I’ve also included a simple bar soap mode for convenience.
If you’ve used my recipes before, the results here should match pretty closely. If not, you can use it as a flexible starting point for your own recipes.
Helpful guides
If you’re just getting started with soap making, these guides will help: