How to Calculate Lye for Soap
How to work out lye and liquid amounts for cold process and hot process soap, and the reasoning behind each setting.
What the calculator does
FormuMate's soap calculator works out precise lye and liquid amounts for cold process and hot process soap. Build a recipe from your oil blend, adjust superfat, choose your water setting, and export the result when you are ready to save it.
Review hardness, cleansing, conditioning, bubbly lather, creamy lather, iodine, and INS before you make the batch. Save recipes, export them to PDF or Excel, and send finished calculations to Sage for formulation feedback.
Common questions
What does the FormuMate soap calculator do?
It calculates NaOH or KOH amounts for soap recipes based on your chosen oils, superfat setting, water ratio, and lye type.
Can I use it for cold process and hot process soap?
Yes. The calculator is designed for both cold process and hot process soap making and supports common oil blends used by handmade soap makers.
Does the calculator support recipe exports?
Yes. You can export your calculated recipe to PDF or Excel after building your formulation.
What is a saponification value and why does it matter?
A saponification (SAP) value is the amount of lye needed to fully saponify one gram of a given oil. Different oils have different SAP values, so a soap calculator uses these values to work out the exact lye amount for any oil blend.
What superfat percentage should I use for cold process soap?
Most cold process soap makers use a superfat between 5% and 8%. A 5% superfat gives a harder, longer-lasting bar, while 8% produces a slightly more conditioning bar. You can adjust the superfat freely in the FormuMate calculator.
What is the difference between NaOH and KOH soap?
NaOH (sodium hydroxide) is used to make solid bar soap. KOH (potassium hydroxide) is used for liquid or soft soap. The FormuMate calculator supports both lye types and automatically applies the correct saponification values.
Do I need to create an account to use the soap calculator?
No. The FormuMate soap lye calculator is completely free and does not require an account or sign-up.